Lake of Brimstone

The Lake of Brimstone is a water-filled volcanic crater in the deep south. It's rather high up and climbing up to it is a difficult task and the surrounding soil is dead and toxic from the chemicals leaking from the volcano.

The lake is almost always steaming from the heat of the water, which is tolerable enough for a human to swim in but certainly not for too long.

In the middle of the lake is an island, however, and apparently on that island is a passageway to a heated labyrinth underneath the lake. Some say there's a trove of magical scrolls and books hidden underneath the lake, a place to keep them safe from the hands of the mad king who demanded anything pertaining to magic be burned and destroyed. Getting to that little island, however, is the challenging part.