WHO LAST SAW THE RING?

This hunt was undeniably a difficult one, so I am going to do what Exeter did at the end of his hunt a few months ago, and explain the verses I gave as the clues for this ring hunt!
You can see the full poem below, for reference.

The Poem: Style, Inspiration and Story
As evident from the very first line - "Eärendil was a mariner" - my poem is inspired by Bilbo's Song of Eärendil (The Fellowship of the Ring, "Many Meetings"). I did not use any other quotes from Bilbo's original song, but I did largely replicate its style and meter.

The first four verses of my poem tell a story, and following it allows discovering the location of the ring.

Verse I
This first verse is an introduction to the story - the story of Eärendil. In this verse I briefly summarise Eärendil's role in the events of the First Age: how he sailed West from Beleriand in search for aid, bearing a Silmaril on his brow; and how he then returned eastwards, soaring through the skies as a flame, bringing hope with him (thus becoming "The Flammifer of Westernesse").

• "East returning": this is, essentially, the only truly meaningful part of this verse - hinting that one should focus on searching in the East, since the "West" that has been mentioned thus far is long gone.

Verse II
Now with the introduction out of the way, and the events of the First Age behind us, the real story begins - the story of Eärendil's endless voyage through the skies of Middle-earth as the star that we now know as Venus. Unlike before, when Eärendil's voyage took him eastwards from Valinor back to Beleriand, now in later ages he must always fly westwards, as do all the stars in the sky.

• "o'er pastures wide": starting his daily journey in the east, Eärendil's voyage takes him over the vastness of Rhûn - the Far East of Middle-earth; this region, at least to an extent, contains large steppes and grasslands - "pastures wide".
• "nigh where fiends abide", "shadowed lands where dwells the Eye": direct referrences to Mordor, which Eärendil approaches from the east.

Verse III
Now that Eärendil flies over Mordor, the narrative draws attention towards a specific area inside the Black Land:

• "the dark and ashen plain": a reference to Lithlad, the Plain of Ashes; although its exact location is debatable, the following clues point in a clearer direction.
• "saddened fields where thralls must toil", "bitter waters": a reference to the "great slave-worked fields away south [...] by the dark sad waters of Lake Núrnen" (The Return of the King, "The Land of Shadow"). The waters of Sea of Núrnen are described as bitter and sad, and Sauron's slaves toil in the fields about them to feed his vast armies.

Verse IV
But Eärendil - powerless to aid the thralls of the Dark Lord beyond giving them hope - cannot linger there, and must hurry on with his endless journey.

• "o'er southern cliffs": this is the final geographical clue in the poem, hinting that the ring is somewhere in the cliffs to the south of Nurn - the the south-west, in fact, if one considers Eärendil's journey always takes him westwards.

Now one might think - this is not enough information to find the ring! And that is true indeed: this is why we need the final verse.

Verse V
The final verse of the poem steps away from the narrative told thus far, and asks the reader to pay close attention to the clue that was hidden in plain sight all along: "the answer plainly hid[den] in every line of this fair lay". The meaning of this should be apparent when you see emphasis I added to the full poem below:

~~~~~~~~~
Eärendil was a mariner
in lands now lost deep under wave;
to West of West he sailed for aid,
his brow bejewelled o'er visage grave;
East returning, bright he came:
lit the skies with ship's white flame.

His star now sails through heavens high
and rides the clouds o'er pastures wide,
renewing hope in weary hearts;
now onward nigh where fiends abide,
ere morning he now hurries by
near shadowed lands where dwells the Eye.

Still, his silent star above
the dark and ashen plain doth rise,
o’er saddened fields where thralls must toil
nigh bitter waters watched by spies,
ere light of morning fills the skies.

Called to sail by silently,
little can he linger there;
in haste he soars o'er southern cliffs,
forgetting not his journey fair,
forever sailing through the air.

Heed the answer plainly hid
in every line of this fair lay;
now the wise will seek with care
the secret words which point the way!
~~~~~~~~~

That's right - I added a sneaky acrostic that runs throughout the poem
Eithel Harnen, Stone Cliff - Eithel Harnen being the Elvish for "source of the river Harnen" (c.f. Eithel Ivrin and Eithel Sirion), Stone Cliff pointing once again to the cliffs (above the source of Harnen). Techincally speaking, if one where to clock on to the acrostic early on, it could've been possible to find the ring right after the second verse!

The final verse's acrostic spells hint, which is exactly what that verse is

So there you have it! It is also funny to note that the chest is visible on the Dynmap, especially in the isometric view:



Well done to all the finders! I hope you all enjoyed this one
(Poster by @Pausi; also credit to @ExeterKered for helping me through a writer's block - composing a poem with an acrostic is not easy - as well as for creating the final verse!)