The Longwood Swallet is a cave near Charterhouse, in the Carboniferous Limestone of the Mendip Hills, in Somerset, England.

The cave is part of the Cheddar Complex SSSI and is connected to August Hole.

Longwood Swallet's entrance is lidded concrete block construction.

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.