These we bought many years ago from GRS

[PDR - Paul owlpool]

Cast concrete, very heavy, and have lasted and weathered well, and fit in with the natural stone quite well

North portal

 

South portal recently in the snow

 

 

 

from the inside - plenty of space - 2 arms length,  solid but can be dismantled for access if necessary

 

 

portal for canal, same source [ Russell pre mods ]

 

 

home made out of recycled wall blocks - mine adit entrance - moss growth after about 10y