Frost Temple

Underneath the vast boundries of Crystal Lake, deep down below where no one usually reaches due to the need of air, there is an underwater temple. When you reach the temple, however, you may be shocked that there is a magic around it that gives you air, despite being underwater, and allows you to breathe the water in normally as if it was air. From there you can explore the temple's beautiful inner chambers. If it wasn't underwater, even if you can breathe, it would be a lovely place to stay in. (Also totally nothing evil in here)