This can be difficult, depending on the number of locked doors that appear. Stocked up on food and craft a useful weapon early to be able to explore faster. With luck, you will have a small amount of locked doors and enough keys. Also, after completing the game you will have access to a perk that allows you to unlock doors without a key. However, it can only be used once every 100 turns. Note: You do not have to kill the monsters in the rooms for them to qualify as explored.