West also built a tunnel from the Observatory to St Vincent's Cave (also known as Ghyston's Cave or Giants' Cave), which opens onto St Vincent's Rocks on the cliff face, 250 feet (76 m) above the floor of the Avon gorge and 90 feet (27 m) below the cliff top.
The tunnel, which is 200 feet (61 m) long, took two years to build at a cost of £1300, and first opened to the public in 1837.

This cave was first mentioned as being a chapel in the year AD 305 and excavations, in which Romano-British pottery has been found, have revealed that it has been both a holy place and a place of refuge at various times in its history.
Although the cave is in limestone, there are few formations in the natural passages.
West also built a tunnel from the Observatory to St Vincent's Cave (also known as Ghyston's Cave or Giants' Cave), which opens onto St Vincent's Rocks on the cliff face, 250 feet (76 m) above the floor of the Avon gorge and 90 feet (27 m) below the cliff top. The tunnel, which is 200 feet (61 m) long, took two years to build at a cost of £1300, and first opened to the public in 1837.
This cave was first mentioned as being a chapel in the year AD 305 and excavations, in which Romano-British pottery has been found, have revealed that it has been both a holy place and a place of refuge at various times in its history. Although the cave is in limestone, there are few formations in the natural passages.
Clifton Observatory