How do teleporters work in Steamworld Dig?

Solution 1:

The teleporter on the surface will bring you back to your most recently used underground teleporter.

To test this, I bought a teleporter from Cranky’s shop and placed it in the Old World (second area). This let me travel between the surface and the Old World.

I then backtracked to the teleporter in Archaea (first area). After using it, the surface teleporter let me travel between the surface and Archaea. This gave the same result after saving and quitting the game.

If you destroy your last used teleporter by digging the ground underneath, the surface teleporter will disappear until you use a another teleporter.