These are the remains of one of Great Britian's seaborne anti-aircraft fortifications. There used to be an elaborate network of walkways and communication lines running between the towers, each of which had a specific job as gun tower, searchlight tower, control tower, etc. There are apparently two such ruins left. You can read about them here.
Reading this article reminded me of another, more detailed, account of a lone kyaker's exploration of Fort Carroll, which is visible from the bay side of the Francis Scott Key bridge in my beloved Baltimore. You can read it here, if you are so inclined.
Stuff like this really intrigues me. I love the idea of exploring long forgotten places. Another interesting site is Forgotten Ohio which Coqui may find interesting since many of the sites listed are in or around Columbus.
Has anyone else got links to good ruin exploration or urban exploration sites? I really don't care where the sites are. I just enjoy reading stuff like this.