Philip Jose Farmer's the Dungeon: The Hidden City/the Final Battle

The Hidden City: Nearing the zenith of their quest, Clive and Neville Folliot and their comrades from time and space are scattered through a ruined city. Beneath the decaying streets waits the greatest danger of all: the Ren and the Chaffri, inscrutable masters of the Dungeon! The Final Battle: Fleeing from the mysterious creators of the Dungeon, Clive breaks through to the ninth level. Stranded in a freezing polar wilderness, he struggles to find his missing comrades and to triumph at last against the murderous masters of the Dungeon!