This is exactly as titled: the way the mine was held open for the miners to gain entry. It didn’t look all that reassuring to me but I haven’t been exposed to an all-wood mine. Anyway, this is over 150 years after the mine opened and the rusty set of cross-hatched handywork was put into place yet it’s still working just fine.
The pipe was either a water pipe (constantly pulling the ground table’s water out of the tunnels) or an air pipe (supplying the miners air and/or removing dust).The other metal you see is the hand rails for tourists to use the steps to a landing that overlooks the main tunnel. Neither was there for the miners.