The swallet is a small, single pothole cave system that is dominated by a series of deep (117 metres (384 ft)) and mainly vertical passages, which follow fault lines, natural joints in the rock and mineral veins. It shows a form of cave development not seen elsewhere in the Mendips and contains the tallest vertical shaft in any known cave on the Mendip Hills, Atlas Pot, which is 60 metres (197 ft) deep. The stream that flows through the cave is one of those that feeds St Andrew's Wells in the grounds of the Bishop's Palace in Wells.
Thrupe Lane Swallet was first entered in 1974 following digging by three caving groups. The entry shaft has been blasted open to ensure a stable entrance.