I visited Beacon Hill Fort recently and was allowed in to explore this fascinating time warp site, unchanged since ww2, the restoration is well under way and huge amounts of undergrowth, trees and debris have already been cleared to open up the buldings and tunnels, there is now a website and Facebook group too with lots of pics
https://www.beaconhillfortharwich.co.uk/
https://www.facebook.com/groups/221891288365384/about/
https://www.justgiving.com/crowdfunding/beaconhillfortharwich