Clairvoyance is an extremely useful ability that lets you get a picture of all nearby rooms that can be reached through obvious exits, at the cost of a few spell points. It will tell you if each room has a monster, player, familiar, or object in it. This helps a lot when keeping away from a wandering or chasing monster, but is absolutely invaluable for getting through mazes quickly. The classic ‘drop coins in each room’ method of maze mapping becomes exponentially more useful when you can instantly exclude every adjacent room you’ve already dropped coins in.
Ducks and minotaurs get clairvoyance, and a few items grant access to it. If all else fails, any player with enough experience can buy it as an ability in an ability room. There is a clairvoyance spell which can do the same thing once per casting, but it is not very useful since it takes 1-2 full rounds to use.
Sample Clairvoyance output:
+---+ Lexicon: | + * = named exit, eg "portal, enter" /.-*+ . = down exit / ^ = up exit +---/ F = Familiar |FPO| P = Player /^--+ O = Object / M = Monster +---/ |M O| +---+