When failing to crack the safe, you will trigger a trap, and a Floor will appear below you. Only after receiving damage, players can right-click the floor allowing 2 options: Examine which says "it's the floor"; and Search, which does not seem to do anything. It is recommended to have some cheap food, e.g. jug of wine to heal with. Re-spawn of the wall safe is mere seconds, making this activity a very fast way to level up. With no failures and fast cracking (one attempt can take from 3 secs up to 10) one could make about 1500 experience points per minute (90k exp per hour). Realistically, it is much less (Around 20k/h)