The only ones that are accessible at the moment are the fuel bunkers/tunnels am d Southwick tunnels which are owned by ucap airsoft there's 5 known entrances to the fuel bunker 3 of which are fully sealed and one I'm trying to locate and one that is open, there's also a deep shelter set of tunnels which have recently been sealed back up which I know of the entrance and currently awaiting them to be reopened by someone lol most of the tunnel complexes in portsdown are fully sealed but there are a few not alot of people know about and also a few vent shafts which lead down to them but are really really right fits