The secret tunnel of Bothwell castle?

Ok so recently i stumbled across a thread about a secret tunnel that is supposedly between the priory at Blantyre and Bothwell castle at Bothwell (link here http://www.secretscotland.org.uk/forum/m-1263574725/s-0/ ) i have now enlisted a friends help  in trying to fine these  tunnels or tunnel  and will be going on this adventure  when the weather turns nicer.

only problem is it is and could possibly be coal mines and if it is then its not exactly a great find as kids have already uncovered these mines. and were resputed to have played in a section of these mines and wound up at the priory end across the river Clyde.

have a look for yourself

clearly pointed out is the sections that are of interest. the donjon and the res broken marked line is a excellent place to start looking for a tunell. along with the old house that is  just  to the side where the trees are bottom right of the bottom right tower.

think a place to start is at the house uncover the mines, then move to the donjon and then down towards the river through the trees and look for anythingt hat seems as if its covered or broken or folded in.