drill

Dig underground in a drill vehicle.

Usage:
  drill down          from the surface (outdoors) or a level deeper, to level -5
  drill <direction>   north, east, southwest... at the same depth
  drill up            a level higher; from -1, back out at the surface

You can go anywhere under built ground. Rooms someone has built underground
(mines, bunkers, old tunnels) are where you can get out; the raw tunnels you
dig fill back in once you've gone. Each dig burns 2 fuel.

Examples:
  drill down
  drill north
  drill up