Another thing. For the sake of continuity and background, I need to know which places your characters have already visited. A fair "selection" of drow cities can be found here:
http://myth-drannor.net/DlabraddathNet/z-sshamath/Societies.htm' target='_blank'>Sshamath - city selection
... including some descriptions, while a nigh complete list would read like this:
Abaethaggar, Abburth, Baereghel, Charrvhel'raugaust, Chaulssin (100 miles west of Citadel Adbar), Ched Nasad (High Gap, Graypeak Mountains), Cheth Rrhinn, Dusklyngh (200 miles north of the Frozen Forest & 100 miles east of Anauroch), Eryndlyn (120 miles east of Illefarn), Faneadar, Guallidurth (70 miles WNW of Calimport), Haundrauth, Ithilaughym, Jhachalklyn, Karsoluthiyl (200 miles west of Baldur's Gate), Llurth Dreier (140 miles west of the northern tip of the Great Rift, Shaar), Luihaulen'tar, Maeralyn (20 miles west of Tharsult), Maerimydra (100 miles west Zhentil Keep, beneath Daggerdale), Menzoberranzan (100 miles west Silverymoon), Orlytlar, Sschindylryn (220 miles north of Elversult), Sshamath (200 miles east of Scornubel), Sshanntynlan, Szithlin, Tlethtyrr, T'lindeth (Dambrath), Tyrybblyn, Uluitur, Undraeth, V'elddrinnsshar (West Galena Mountains), Waerglarn, Waethe Hlammachar, Yuethindrynn
Most of these cities (as in: all that haven't got an entry in the link above) have no description or not even a place on the map of Faerûn. Make sure that your choice is reasonable, regarding distances and all. And remember that there might be the odd non-drow city/settlement that your character might have visited too.