Geography of Middle Earth

[Tuor in Gondolin]

Karen Fonstad's The Atlas of Middle-Earth has some
interesting conjectures. About Cuivienen , she has a
rather giant Inland Sea Of Helcar extending from about
where 2nd, 3rd age Mordor is far to the east with Cuivienen on
the eastern shore, in distance about 2x again the distance from
the western edge of Beleriand to the Ered Luin.

And in the Encyclopedia of Arda:

This map of Cuiviénen is adapted from Map IV from The Shaping of Middle-earth (volume 4 of The History of Middle-earth). It is unclear how much of the detail of that early map Tolkien meant to stand, but it is the only source we have that shows Cuiviénen in any detail. Certain elements of the map shown here have been modified to bring it into line with the published Silmarillion - see Note 1 for details.
Called the Water of Awakening, the land on the shores of the inland sea of Helcar where the first Elves awoke during the Years of the Trees; it lay far in the east of Middle-earth.

The map referred to above didn't come out (sorry).