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 block(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 (with varying abilities) in the Underworld. After you defeat the Wall of Flesh, then a Mimic chest (an enemy that appears as a Shadow Chest until approached).