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.
The players see a small shrine to the local nature deity just of the trail. Before they even approach it, they can smell the foul stench of rotting meat. If they inspect the shrine, they can see it has been desecrated by rotting organs in the last few days. There is no mistaking it for an obscure ritual, the organs are thrown everywhere, not left in specific places as in sacrifice.
If the players try to clean the shrine, they will soon find it has been boobytrapped to fling sharp splinters covered in the rotting gore in every direction. While only doing a few points of damage, they injured players will likely take sick soon unless they get medical attention.