Philip José Farmer's the Dungeon

The return of a classic "shared world" fantasy series created by Philip Jose Farmer, award-winning author of the "Riverworld" saga! Plunging into a vast prison that spans a planet, Clive Foliott faces a fantastic world of dwarves, cyborgs, and aliens unlike anything he has ever imagined. It is a multi-leveled collection of beings from the hidden folds of time and space. Trapped somewhere inside is Neville Foliott, Clive's twin brother, and no creature in the Dungeon will stop Clive from finding him...