Day 3 (evening): Added lava rivers which hurt! unless you are a fire elemental. Played with tcod noise generation without success, so the rivers follow a simple snake which randomly turns a bit left or right. It's nice but easy for the player to get stuck. Making sure the exit is on the same side of the river as the player could be an option.
I will try to implement 5 or 6 challenges like the lava river and pick one per level.