Tremorsense

Tremorsense was a type of sense that a few kinds of creatures had. Creatures with such a sense could detect and precisely locate vibrations, including those of other creatures. Creatures with tremorsense had to be in contact with the source of the vibrations, that is, via the ground, thus it couldn't be used to detect flying or incorporeal creatures.

Creatures known to have had tremorsense include:
 * Bulette
 * Black pudding
 * Cavelord
 * Purple worm
 * Earth elemental
 * Flail snail
 * Frost salamander

Spell
Some mages could cast the tremorsense spell, giving them temporary access to this sense.