Evernight

We have only the vaguest description of Evernight, so we cannot be sure where its boundaries lay. Hyarmentir was a peak that lay to the south of Valinor, which therefore places it in the same general region as Evernight, and so we might reasonably imagine it as lying within that area, though it is impossible to state this with certainty.

The reason that Evernight was associated with endless darkness is not explained. It presumably lay eastward of the Mountains of Defence, and would therefore have been shadowed from the Light of the Trees during the time they shone in Valinor. That offers a possible explanation for the name's origins, though when Eärendil passed through this region the Trees were long gone and the Sun would have shone down on the land, so 'Evernight' seems an odd description. We know that Ungoliant had dwelt in the southern lands in ages past, and webbed the mountains in darkness, so perhaps this offers an alternative reading of the name's meaning.

We have very little detail about the location of Evernight or Night of Naught, so this map is necessarily approximate. Tolkien's expanded index to The Lord of the Rings tells us that it lay far to the south of Valinor, and the "Song of Eärendil" describes Eärendil travelling over roaring waves as he passed through the region. So, Evernight must have been in the approximate area shown here, and at least partly covered by the ocean (if indeed it did not form a sea in its own right).