In Blazeridge (40-50) there is an area called Behem Gauntlet. There is a jumping puzzle here. A friend and I were erroneously trying to solve this puzzle by going through a waterfall in the southeast part of this area. This passage led to a underwater passage that seemed to lead to nothing. We eventually found a small crack in the passage that led us out and under the entirety of Blazeridge. We were still swimming and the terrain above us was colored with blue hues. We didn’t venture far as we knew this wasn’t part of the puzzle and probably shouldn’t exist for players. I have added a few screenshots of what it looked like. If you need any further info, let me know.
