https://www.openstreetmap.org/way/674265745

bridge=culvert? What is the intended meaning of this tag?

I am aware about tunnel=culvert for water piped under road (usually streams/drains) - see https://wiki.openstreetmap.org/wiki/Tag%3Atunnel%3Dculvert

Start

The path should connect to the road, else the navigator gives very funny itineraries.

Grindstone Cave

Marble Baths Cave

This is misplaced. The actual pass is up on the mountains west of here.