An atmospheric substance called air, and a quite fuggy variant on that, is my guess .

He claims to have explored 200m of tunnels and stopped where there was a T split. There are "stories" of children entering the small pyramid tunnels and coming out on top of the large one on the other side of the river. Perfectly dry tunnels underneath a river after 12000 years - amazing...

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To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.