The poetess from Lichfield met the Ladies in 1795. In her published correspondence (1811; 6 vols.) there are several letters to Sarah and/or Eleanor, though, of course, her letters about the Ladies were written to others.
Anna Seward (1742-1809) – The six-volume Letters of Anna Seward written between the years 1784 and 1807 appeared in 1811. Volumes 4, 5, and 6 include letters to the Ladies of Llangollen. The most impressive, however, in terms of first-hand accounts of the Ladies, were sent to the Rev. Henry WHITE of Lichfield, the letter dated Barmouth, September 7, 1795; and to Mrs. Parry PRICE of Chester, the letter dated Lichfield, October 15, 1795. Their aeolian harp (and Seward’s production of one for her own use) is described in the letter to Miss WINGFIELD (vol. 4; letter XLVII).
Unfortunately, letter-writers write letters about themselves, so web-readers may learn more about Seward herself when she addresses letters to Eleanor and Sarah.
Pertinent letters are slowly showing up on the blog [see below] (I transcribed thirty-five of them)!
To whet the appetite, here’s the first, from vol. 4, Letter XX, pages 98-109:
The Rev. Henry White, of Lichfield.
Barmouth, Sept. 7, 1795.
I resume my pen, to speak to you of that enchanting unique, in conduct and situation, of which you have heard so much, though, as yet, without distinct description. You will guess that I mean the celebrated ladies of Langollen Vale, their mansion, and their bowers.
By their own invitation, I drank tea with them thrice during the nine days of my visit to Dinbren; and, by their kind introduction, partook of a rural dinner, given by their friend, Mrs Ormsby, amid the ruins of Valle-Crucis, an ancient abbey, distant a mile and a half from their villa. Our party was large enough to fill three chaises and two phaetons.
We find the scenery of Valle-Crucis grand, silent, impressive, awful. The deep repose, resulting from the high umbrageous mountains which rise immediately around these ruins, solemnly harmonizes with their ivied arches and broken columns. Our drive to it from the lovely  villa leads through one of the most picturesque parts of the peerless vale, and along the banks of the classic river.
After dinner, our whole party returned to drink tea and coffee in that retreat, which breathes all the witchery of genius, taste, and sentiment. You remember Mr Hayley’s poetic compliment to the sweet miniature painter, Miers:
“His magic pencil, in its narrow space,
Pours the full portion of uninjur’d grace.”
So may it be said of the talents and exertion which converted a cottage, in two acres and a half of turnip ground, to a fairy-palace, amid the bowers of Calypso.
It consists of four small apartment; the exquisite cleanliness of the kitchen, its utensils, and its auxiliary offices, vieing with the finished elegance of the gay, the lightsome little dining-room, as that contrasts the gloomy, yet superior grace of the library, into which it opens.
This room is fitted up in the Gothic style, the door and large sash windows of that form, and the latter of painted glass, “shedding the dim religious light.” Candles are seldom admitted into this apartment. –The ingenious friends have invented a kind of prismatic lantern, which occupies  the whole elliptic arch of the Gothic door. This lantern is of cut glass, variously coloured, enclosing two lamps with their reflectors. The light it imparts resembles that of a volcano, sanguine and solemn. It is assisted by two glow-worm lamps, that, in little marble reservoirs, stand on the opposite chimney-piece, and these supply the place of the here always chastized day-light, when the dusk of evening sables, or when night wholly involves the thrice-lovely solitude.
A large Eolian harp is fixed in one of the windows, and, when the weather permits them to be opened, it breaths its deep tones to the gale, swelling and softening as that rises and falls.
“Ah me! what hand can touch the strings to fine,
Who up the lofty diapason roll
Such sweet, such sad, such solemn airs divine,
and let them down again into the soul!”
This saloon of the Minervas contains the finest editions, superbly bound, of the best authors, in prose and verse, which the English, Italian, and French languages boast, contained in neat wire cases: over them the portraits, in miniature, and some in larger ovals, of the favoured friends of these celebrated votaries to that sentiment which exalted the characters of Theseus and Perithous, of David and Jonathan.
 Between the picture of Lady Bradford and the chimney-piece hangs a beautiful entablature, presented to the ladies of Langollen Vale by Madam Sillery, late Madam Genlis. It has convex miniatures of herself and of her pupil, Pamela; between them, pyramidally placed, a garland of flowers, copied from a nosegay, gathered by Lady Eleanor in her bowers, and presented to Madam Sillery.
The kitchen-garden is neatness itself. Neither there, nor in the whole precincts, can a single weed be discovered. The fruit-trees are of the rarest and finest sort, and luxuriant in their produce; the garden-house, and its implements, arranged in the exactest order.
Nor is the dairy-house, for one cow, the least curiously elegant object of this magic domain. A short steep declivity, shadowed over with tall shrubs, conducts us to the cool and clean repository. The white and shining utensils that contain the milk, and cream, and butter, are pure “as snows thrice bolted in the northern blast.” In the midst, a little machine, answering the purpose of a churn, enables the ladies to manufacture half a pound of butter for their own breakfast, with an apparatus which finished the whole process without manual operation.
The wavy and shaded gravel-walk which encircles  this Elysium, is enriched with curious shrubs and flowers. It is nothing in extent, and every thing in grace and beauty, and in variety of foliage; its gravel smooth as marble. In one part of it we turn upon a small knoll, which overhangs a deep hollow glen. In its tangled bottom, a frothing brook leaps and clamours over the rough stones in its channel. A large spreading beech canopies the knoll, and a semilunar seat, beneath its boughs, admits four people. A board, nailed to the elm, has this inscription,
“O cara Selva! e Fiumicello amato!”
It has a fine effect to enter the little Gothic library, as I first entered it, at the dusk hour. The prismatic lantern diffused a light gloomily glaring. It was assisted by the paler flames of the petit lamps on the chimney-piece, while, through the opened windows, we had a darkling view of the lawn on which they look, the concave shrubbery of tall cypress, yews, laurels, and lilachs; of the woody amphitheatre on the opposite hill, that seems to rise immediately behind the shrubbery; and of the grey barren mountain which, then just visible, forms the back ground. The evening-star had risen above the mountain; the airy harp loudly rung to the breeze, and completed the magic of the scene.
 You will expect that I say something of the enchantresses themselves, beneath whose plastic wand these peculiar graces arose. Lady Eleanor is of middle height, and somewhat beyond the embonpoint as to plumpness; her face round and fair, with the glow of luxuriant health. She has not fine features, but they are agreeable; –enthusiasm in her eye, hilarity and benevolence in her smile. Exhaustless is her fund of historic and traditionary knowledge, and of every thing passing in the present eventful period. She has uncommon strength and fidelity of memory; and her taste for works of imagination, particularly for poetry, is very awakened, and she expresses all she feels with an ingenuous ardour, at which the cold-spirited beings stare. I am informed that both these ladies read and speak most of the modern languages. Of the Italian poets, especially of Dante, they are warm admirers.
Miss Ponsonby, somewhat taller than her friend, is neither slender nor otherwise, but very graceful. Easy, elegant, yet pensive, is her address and manner:
“Her voice, like lovers watch’d, is kind and low.”
A face rather long than round, a complexion clear, but without bloom, and with a countenance  which, from its soft melancholy, has peculiar interest. If her features are not beautiful, they are very sweet and feminine. Though the pensive spirit within permits not her lovely dimples to give mirth to her smile, they increase its sweetness, and, consequently, her power of engaging the affections. We see, through their veil of shading reserve, that all the talents and accomplishments which enrich the mind of Lady Eleanor, exist, with equal powers, in this her charming friend.
Such are these extraordinary women, who, in the bosom of their deep retirement, are sought by the first characters of the age, both as to rank and talents. To preserve that retirement from too frequent invasion, they are obliged to be somewhat coy as to accessibility.
When we consider their intellectual resources, their energy and industry, we are not surprised to hear them asserting, that, though they have not once forsaken their vale, for thirty hours successively, since they entered it seventeen years ago; yet neither the long summer’s day, nor winter’s night, nor weeks of imprisoning snows, every inspired one weary sensation, one wish of returning to that world, first abandoned in the bloom of youth, and which they are yet so perfectly qualified to adorn.
Travelling hither, we found the country rising  into yet bolder and sublimer beauty on our progress — the mountains more vast, and more magnificent that night of woods which generally clothes them; though sometimes they aspire the clouds in the grey grandeur of barrenness — while nothing was ever so richly umbrageous as the vales and the glens at their feet, interspersed with meads of the freshest verdure, and with rocks that thrust their craggy points, and lift their angular eminences, whose sterility finely contrasts the woody luxuriance of the general scene. The Deva, always visible, and drawing his “wizard waters” in lines of light, from his rising out of the Lake Bala, through the long track of beauteous vales, Llandynion, Landesillis, Valle-Crucis, and Langollen, extending at least twenty miles. So unpropitious, however, was the wet and cheerless day, that it was through shrouds of rainy mists that we but in part discerned this all-surpassing scenery beneath, as our road zoned the midway of the Alpine steeps which overhung it.
We slept at Bala the first night, that boasts her silver lake eleven miles in circumference. Another rainy morn — but it soon cleared up after we had resumed our journey. We found the road comparatively dreary during about eight miles; –the mountains were vast, but uniformly barren, and the vales at their feet had little luxuriance;  but during the remaining ten miles, that lead us to Dolgelly, romantic Beauty resumed all her empire, with the sublime addition of cataracts thundering down the rocks. These were the present of our late rains. One of them was super-eminent in grandeur and picturesque grace. In the dark recess of some immense and over-arching rocks, two large and roaring torrents met, which had descended from their sides, and spread wide sheets of snowy foam in the gloomy chasm.
Waiting for horses at Dolgelly till after five, they at last gave us tired ones; and I have since learned that they were stone-blind. A circumstance so cruel involved us in perils that might have appalled a stouter heart than mine. In the midway to Barmouth night overtook us. Then it was that our miserable horses refused to draw on every ascent, standing stock still, insensible alike to the coaxing or the lashes of the driver; and this though we always alighted, creeping on the foot up every hill, with immense fatigue to me, and with terror inexpressible.
But for one fortunate circumstance, amid those wild and savage heights must we have passed the night, stunned with the din of unseen torrents, pouring down the rocks above — a noise which darkness rendered horrible — while intervening seas were breaking in at the feet of those precipices on  whose edge we travelled. –Fortunately we met with two stout peasants, who, by our bribing high, were induced to accompany us to Barmouth, to assist the horses in dragging the empty chaise up the hills, and to walk between our horses and the precipices when we were in our vehicle. Luckily it did not rain, though the infant moon was shrouded in threatening blackness. The road, by day-light, is not very unsafe, though sufficiently alarming. It leads through magnificent scenery of rocks and woods, interspersed with arms of the sea, and the ocean lying in front, –but the veil of night concealed its charms from us, and trebled all its dangers. Ah! how welcome the glimmering lights of the Barmouth windows. –It was eleven ere we arrived. From a projection of the rocks, there was no appearance of human habitation till we immediately descended into the town. Nothing, till then, could our wearied eyes discern through the gloom, but a vast ocean, howling and harbourless.
I must not conclude my letter without observing, that, on my second visit to the fairy palace, a lovely Being cast around its apartments the soft lunar rays of her congenial beauty. — Mrs Tighe, the wife of one of my friend’s nephews, an elegant and intelligent young gentleman, whom I should have observed more had his wife’s beauty been less. I used the  word lunar as characteristic of that beauty, for it is not resplendent and sunny, like Mrs Plummer’s, but, as it were, shaded, though exquisite. She is scarcely two-and-twenty. It is not too much that Aonian inspiration should be added to the cestus of Venus? She left an elegant and accurate sonnet, addressed to Lady E. Butler and her friend, on leaving their enchanting bowers.
Lady Cunliffe, of whom you have often heard me talk with delight, was here for a day or two the beginning of the week. We met as old friends. She is the same intelligent, interesting, amiable creature with whom I passed a month so pleasantly at Buxton in the autumn 1784 — but eleven years have made some havock in her beauty; — unless the swart power of these fierce suns, exposed to them during several days, as she had been, in an open carriage, and the dust and dishabille of travelling, had greatly increased the tarnishing power of time. Seeing her now, you would say she was a very fine woman; but would scarcely conceive how divinely handsome she was at the period above mentioned. Her lilies and roses are exchanged for the unblended flush of sun-burnt health. Ah! if my dear Honora, whom she then so strikingly resembled, had lived to this hour, she would probably have been as much, perhaps more, altered. It is these changes that make it so desirable  to possess good pictures of our lovely friends, before time shall either fade or bronze them. If, like my sister and Honora, they die young, their beauty lives, in undecaying youth, in the memory of their contemporaries; but if they grow old by our side, we insensibly lose the distinct recollection of what they once were, without the assistance of the pencil.
This bright morning has risen upon me with better health on its wings. I have accepted the very kind offer of Mr Wise and his engaging daughters, and am settled in delightful apartments, situate on an high terrace, that looks immediately down upon this vast mass of animated water. I sit writing at an open sash-window, inhaling its salubrious gales. The tide is flowing up, and rolls its green waves in light.
What mercifully fine weather is ripening the golden harvest that waves through our land! O! that to this gracious boon of Heaven, our rulers would endeavour to add the blessings of peace! –that, of all the allied powers, the English would not be the last to grow wise, and bide the sanguinary sword sleep in its scabbard!
**web author’s note: the Lady Cunliffe mentioned here is, alas, not Mary Lady Cunliffe (widow of Sir Ellis Cunliffe, and maternal grandmother of Mary Gosling); but the former Harriet Kinloch, wife of Sir Foster Cunliffe, the 3rd baronet — who inherited the title from his father, Sir Robert — brother of Sir Ellis, who had fathered two daughters (the future Eliza Gosling and her older sister Mary Smith).