Broadwater Down is again accessible via one of the blockhouses (some pretty sharp edges though), but the water is higher than the roof of the tunnels at the moment and coming up the steps. If it's a dry summer it could be good though, but even then will still need waders or an Explorer kamikaze-boat
Subterranea Britannica: Sites: tunbridge_wells_underground_battle_headquarters
Subterranea Britannica: Sites: tunbridge_wells_underground_battle_headquarters