It is 1.65 km in length and reaches a depth of 175m.[2]
The cave was discovered in September 1944 by boys from Sidcot School.[3]
The picture shown is not the Longwood Swallet, it is Longwood Valley Sink. Longwood Swallet's entrance is lidded concrete block construction. A (non-free) picture of Longwood Swallet entrance is available here
The cave is locked and access is controlled by the Charterhouse Caving Company. There is a warning sign posted at the entrance to the cave about flooding. This has always been a problem, but is more pronounced due to the extraction of water from the spring at Charterhouse. When the pumps owned by Bristol Water stop this can cause a flood wave to travel down the stream and into the cave.[4]