Gehennom contains a large number of maze levels. Maze levels always fill the map, unlike dungeon levels, and you can only map a few squares per turn by wandering around. Digging is slow, because wands or spells of digging can only dig 1 square per-shot on a maze level. This has given Gehennom a reputation as a slow and boring phase of the game. But the amount of work involved can be greatly reduced by good strategy.