Nope, no thank you, I'm good on that.
Oh Heck No: Guy Goes Through Water Tunnel In Rock

This is a video of some lunatic taking a trip through a natural siphon created in the rocks of a river. Who was the first person to try this? How did they know they would fit? Honestly, I half expected this guy to never reappear, just push the dead body stuck in there out and take its place, like children getting stuck in a tube slide.