Halliggye Fogou is one of the best surviving examples and is situated within an earthwork enclosing a settlement, possibly a defended Iron Age homestead on the Trelowarren Estate, according to Heritage Gateway.
Unusual UK tunnel shrouded in mystery that is open to the public for free Mystery shrouds an ancient tunnel built more than two millennia ago.
The Iron Age underground chamber is believed to have been built in around the 4th and 5th century BC, and was used for at least 700 years.
It is a large, sprawling complex including a 20 metre long stone-lined chamber with a 28 metres long curvilinear passage branching off it, leading to a much smaller side chamber.
Some archeologists have speculated that the caves were used to store valuables, while others argued that they served as refuges, or used for ceremonies and rituals.
