Sac Actun Cenote cave system in Tulum Mexico. You have to swim into this area to photograph it. Knowing this before hand I held my camera above my head and swam it into the system for the photo. Sac Actun is much larger than just this area and by the afternoon my camera felt like it was 100 lbs trying to hold it above the water. Still glad I did it but next time I think i would bring a floatation device for my arm.