Looking inside.

I would probably want to wear rubber boots here.

Upstream is nicer.

A second branch.

This cliff face stands between the two upstream channels.

And that is the entrance.

Please remember that these photos are all copyrighted to me. If you want to use them in any way, there's a 90 per cent chance I'll give you my permission, and be able to give you a copy with a higher DPI.
Copyright Daehanmindecline 2018