Detect Creatures was a level 2 Divinations spell which allowed you to see monsters located beyond your field of vision within a certain radius. It wasn't entirely accurate, however; positions could be off by a tile, and it would only display the type of monster, not the specific monster (Sigmund would be displayed as a human, an anaconda would be displayed as a snake, etc.). The spell would also reveal mimics.
It was formerly found in the following spellbooks:
Detect Creatures was removed in 0.6 with the removal of the Divinations school of magic.