The Sinister Spire describes an underdark city the the necromancers tower that is in it. The adventure is the second part of the 3 part series though it can easily be played on its own. The Adventure covers getting to the underark city of pedestal, The city its self, an island of luminescent fungus, and the Spire its self. This adventure can also be used just for the underdark city.
E2, following up on Death's Reach, the PC's first travel to Sigil following the smuggled remains of the primordial Timesus. The pursuit then leads into the Abyss, through the White Kingdom to face Doresain, the Ghoul King, exarch of Orcus. The module certainly is epic, placing the PCs up against powerful monsters like greater demons, death knights, and a demilich. It may be frustrating that the PCs arrive too late to disrupt the plot (have to allow for the finale in the next adventure) but taking out Orcus' right hand ghoul may be satisfying. Includes a skill challenge for crossing a portion of the Abyss For environments, City refers to Sigil.