Bromine Lake is a lake that is almost a very small inland sea. It is also special for other reasons. It always has the warmth of a living Human, no matter what the season. It is not a hot spring with its sulfuric chemicals. There are hundreds of theories, but no answers.
Even if they did, they would never believe it, as it has ties to the time of legends, to the time of Corvus.
A small, primitive village has yet to discover fire, which is a good thing because there are highly flammable (but not otherwise dangerous) gasses in the air. The heroes, blissful in their ignorance, don't know that and think it a wonderful idea to show the locals open flame.