Lost Drain Tunnel
Big shout out to Simon for finding this tunnel. For some reason, I was thinking it was last accessible in 2019 but realised it was actually 1999. Pretty sure. I definitely can't give this one out to a single soul as I promised Simon but it's located pretty close to the beach and I remember there was a second one like this one not too far off. Oneday, I'll make the time and effort and see if there's any sign of it, if I can remember roughly where it was located.
Many war tunnels from 'back in the day' - presumably around World War 2 - have since been either sealed or repurposed as drains. I'm not sure what the story of this one is.