The geology of the sewers -- I. The early caves. Quest for the inner sanctum : Carver's Cave at midnight ; A wild goose chase through the sewers : the hunt for Fountain Cave -- II. Buried rivers. The urban Nile : the subterranean streams of St. Paul ; Among the Spice Islands : Minneapolis's underground rivers -- III. The great sandbox. The cave under the castle : Brewery caves ; The medieval temples of Mushroom Valley : St. Paul's west side ; Velvet underground : abandoned sand mines -- IV. The milling district. Subterranean Venice : Minneapolis's mill tunnels ; Boat ride to oblivion : Chute's Cave ; Down the rabbit hole : Nicollet Island caves -- V. Utilities. A lonely day under the mortuary : the Fort Road labyrinth ; Behind the silver door : utility labyrinths -- VI. Pluto's kingdom. Lost world : Schieks Cave ; The big white : Channel Rock Cavern.