Compass

The Compass is a Hardmode Accessory that displays your lateral position to the East or West of the center of the map in 1/2 block (1 foot) increments, when equipped. The center of the map is usually very close to the initial spawn point, but they do not always coincide.

Compasses are dropped by any kind of Mimic, which can spawn during Hardmode anywhere under Level depth, or even higher anywhere where there are dirt walls in the background.

Trivia

 * The sprite used appears to be a reference to the Legend of Zelda series by Nintendo where the Compass is an item obtained in most dungeons.