We went diving in Apoyo lake which is located inside of a volcano crater. It was a really fascinating dive! The visibility wasn't crystal clear and we didn't see too many fish but the most unique part was experiencing the volcanic warmth in the lake floor. We felt the thermal waters flowing after the dive guide would stab the lake floor with a large stick to create a hole. We also experience large air bubbles when you would press hard on the lake floor with your hands. The air bubbles would have smelled strongly of sulfur but we didn't notice since we were underwater with our scuba regulators in. It was a really interesting experience and something quite new for us!