Eilistraee has hardly any temples on the surface. So, with the exception of the Promenade, I don't think she has any temples at all underground. Devotees in the Underdark wishing to worship her probably do so at carefully hidden, secret shrines and such. Shrines, or so I imagine, Eilistraee probably has plenty of.
Either way, you can find a hint of a description [url=
http://www.wizards.com/default.asp?x=dn ... a:21efiw7b]here[/url:21efiw7b] as to what a temple would look like.
[quote:21efiw7b]Temples of the Dark Maiden are typically established in the mouths of dark caverns and in dim forests on the surface world from which her clerics can venture forth at night to brave the moonlight. It is rare for clergy of Eilistraee to found a temple below the surface. The Dark Maiden's clergy seek out pristine, natural sites that need little modification. These places of worship are developed much like those dedicated to the Seldarine. Temple complexes typically include a glade in which to dance, offering an unobstructed view of the moon, and a sheltered place away from the light of day (often an access tunnel to the Underdark). Other common features are a thick tree canopy, a lively freshwater stream, a forge and smithy, and a vein of iron or some other metal suitable for the crafting of swords. However, the simplest shrine of the Dark Maiden requires naught but a moonlit glade and a song (audible or imagined) that draws one into a dance.[/quote:21efiw7b]
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Shir'le