You control an astronaut who ventures through caverns beneath a planet. Climb ladders and move from floor to floor avoiding alien creatures. Trap the aliens by digging holes for them to fall into and then hit them over the head to eliminate them.
On each level, your oxygen supply is limited. After you dig holes, you must lure the aliens into them to trap them. As you go to higher levels, you will have to dig two holes, perfectly placed, one above the other, to keep an alien in.