I've always loved photographs that are about light and shadow. I wasn't expecting this opportunity so unfortunately no tripod and probably some camera shake at 1/30s even holding my breath. This is version (a). Version (b) has a +2 stop burn to the tunnel entrance area. Both have a dodge lower 1/3.
This fort was completed in 1860 in response to fears of a French invasion. There is a vast network of forts around the UK. There are 27 around the Portsmouth area alone. None was ever used because the French suffered a resounding defeat in the Franco-Prussian war of 1870. The structure on the right of the tunnel is an ammunition conveyor. The tunnel decends steeply and continues for hundreds of yards. I took various pictures of gun emplacements which I will try to print in due course.