Caverns of Io is a retro "(extended) ASCII text mode" arcade/shooter.

You have been sent to explore Io, tasked with exploring each cavern in search of potential resources to mine. Armed with a simple cannon, your goal is to explore all thirty caverns, and clear them of any hostile ships.

Each level presents unique terrain and challenges. To survive, you'll need to learn to use each cavern's features to your advantage.

Press the ARROW KEYS to move your ship, and hold WASD keys to fire. You can stop your ship by pressing the arrow key in your current direction of travel.

To open the door to the next cavern, each enemy must be cleared. Later enemies have tough shields, so be sure to save your cannon's valuable energy.

Hints and tips:
- Some enemies will patrol walls, while others will hunt you down.
- Striking a hostile laser shot with your own will cancel both shots.
- Enemies have limited energy, too. If you can coax an opponent to drain its cannons, you'll have a much greater chance of surviving a close-range shootout.
- At 50,000; 100,000; 200,000; 400,000 points, and so on, you can obtain an extra life. The next shield recharge after crossing a milestone will award one extra life.
- When killed, an opponent may drop a recharge power-up. Engage powerful enemies first, and strike weaker ones down if you need a boost.