Step 1: set up a starting chamber, make it 60'x40' with 4 doors leading out and a stairway back to the surface.
Step 2: open a door: Check the locked/trap status of the door Locked or Trapped?, then each time you open a door roll on the “What's behind the door” Table below.
| d20 Roll | What's Behind the Door | Size | Number of Exits |
| 1-5 | Corridor, random direction | 3d4x10' | 1d4 |
| 6 | Closet | 5'x5' | 0 |
| 7 | Small Room | 10'x10' | 1d4-2 |
| 8-11 | Room | 20'x20' | 1d4-1 |
| 12-17 | Chamber | 30'x30'or 40'x40' | 1d4 |
| 18-19 | Large Chamber | 50'x50' or larger | 1d4 |
| 20 | Stairs | 1 flight | 1 –up or down 1 level |