I've now completed the game, but I never found keys to open the 3 locked doors on Level 12: The Prison. They all have keyholes, but I've found no keys for them.
How can I open these? What's behind them?
I was wondering this too, so after I finished the game I did a bit of mucking around, mainly slaying monsters that spawn during the boss-fight, after doing this for a few minutes I noticed one of the keys on the ground.
After that it didn't take long to find the other two, I believe they drop from the Ice Lizards, but not 100% sure
Doors contain: Door 1: 1x lightning rod Door 2: 1x sack, containing 4 health potions Door 3: 4x lightning bombs