Someone on a boat last year was telling me about how he had dived a tunnel near Lulworth Cove and he had video to prove it. So after the first dive on the Aeolian Skye this weekend, we went to look for it as a second dive. We were on a boat, but you could probably do it from shore and we were dropped near the west corner at the entrance to Lulworth Cove. We descended then came to the foot of the cliff in about 5m. Swimming westwards, eventually we found ourselves in a gully with the cliff on the right, and a ridge of rock going up to about 2m on the left.
Then we came to the tunnel entrance at around 5.5m. There's a lot of life around the entrance with spider crabs covered in weed, but as you go further in, it becomes more devoid of life. It goes in quite a long way, getting shallower. I'd estimate it's about 30m long, but it is hard to tell. At the far end, there was a small opening at the top, which you might have been able to get out of, but given the wave action, I didn't try. It's wide enough for two divers to swim comfortably side by side.
Coming back outside the tunnel, we finished our dive in the kelp and rocks there, which harbour a variety of life