Our last play session with me as rotating DM ended with the party about to enter the (classic Greyhawk version) Vault of the Drow. Currently, I am a player in another DM's game, but when it cycles back around to me, the party will indeed be entering and proceeding to the Black Tower.
Several weeks ago I read somewhere about an inn called something like the 'crowned cap' where Underdark foreigners and surface dwellers stay when they are in a certain drow city (I don't think the city was specifically Erelhei-Cinlu but don't remember). There was, if I recall correctly, even a floor plan of the inn included in the source material. Regardless of where it is from, I had planned to drop this inn into Erelhei-Cinlu and have the Bailiff of the Black Tower recommend the party stay there.
Unfortunately, in the time since reading it, I have lost reference to whatever source I found this in. I know it is not in the original first edition D3 description of the city, nor in the third edition version presented in Dragon 298. Neither is it in the third-party Rise of the Drow. I am pretty sure the inn is not specifically tied to Erelhei-Cinlu, as it is not mentioned in the greyhawkwiki for the city, so it is likely a generic 'drow city', but is possibly some version of Menzoberranzan.
Any help in identifying the source for my recollection of something like the 'crowned cap' inn would be appreciated.