Compass

The Compass is an accessory item which when equipped, will display your position to the East or West of the spawn point in 1/2 block (1 foot) increments. It is used at a Tinkerer's Workshop with a Depth Meter and a Gold Watch to craft a GPS. It can be found by killing Mimics in the Underworld, which only spawn after the Wall of Flesh has been defeated.

Note: You may also spawn the Mimic early by wiring up a Chest Statue to a power source (e.g. a Switch, Timer, and so on) and activating the power. Please be careful about spawning them too early - your weapons may be largely useless against the mob.