In the cave systems below Gorodzuba, the mineralized water which seeps from the mountains flows in underground rivers. Recently, the health properties of that water lead to it being actively exploited by a series of pump facilities deep underground. These facilities were often hot, sweaty, and dangerous. When the party came to the facility, it was... degraded. The workers had been attacked and turned into zombies, an attack caused by Koshchey.
As you can tell from the differently colored pipes, there was a pipe puzzle on this map, which is fun! Definitely the sort of thing I should have planned out on paper, because the actual complexity of the puzzle was a little low.
They met with an investiture of Koshchley, the mysterious puzzle maker behind the world's often elaborate and mysteriously durable puzzles. Within the body of a zombie, he was caught unawares, and offered to fight the players later if they promised to tell anyone they came across that they had fought and it had been, like, super tough. In exchange, he would provide them with a level up.
Unfortunately, his ultimate boss battle got cut. Shame!