Chile Easter Island Orongo near Volcan Rano Kau

Birdman competitors had to clamber down the sheer cliffs, swim 3 km through shark infested waters to Motu Nui (1st of 3 islets), grab the first tern egg laid, swim back through the sharks and scale the cliffs. The leader whose representative won this competition was appointed leader of the island for that year. This means of selecting leadership went on from ~1580 to 1866.

To me, this petroglyph looks like a creature from outer space.

I could barely fit a leg through these openings but the Rapa Nui natives were typically 7 feet tall. I don't know how they managed to get inside.