I reconnoitred the Inmosthay Quarries, roughly in the middle of Portland, recently. (There is a rather ill-defined right-of-way I THINK across the area from Wide Street to Easton Lane; other parts were visible from the surrounding land).
Nothing of any speleological interest left. The whole area, including a near-isolated meadow "island" called Fancy's Beach, has been excavated and partially back-filled.
Over the years these quarries had intercepted and fragmented a phreatic network into individual caves: Sawmill Cave, Devil's Hole, Horseshoe Hole and Engineers' Dig (my first digging attempt in the 1970s, along a complete choke of finely-varved sediment!). None of the caves could be considered "sporting" but were of technical interest, with interesting and elegant passage topographies.
Also a fissure-cave, Devil's Slit. Quite what that was doing there so far from the cliffs is anyone's guess! I suppose it might not have been a mass-movement cave after all, but a major joint solutionally-widened by water percolating through its thin roof and trickling down the walls, though it displayed no obvious karst features.
Anyway, all are now gone, and I had great difficulty even identifying main locations among the ruins.
I did find a massive, light brown stalagmite. The quarrymen had removed it from some unknown location and laid it down by the track, next to a sign-post bearing a rough map showing you vaguely the route of the R-of-W. I've no idea what they'd intended but Nature was beginning to give it a shroud of brambles.