Great Blue Hole
The Great Blue Hole is a giant marine sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll from the mainland and Belize City. The hole is circular in shape, across and deep. It was formed during several episodes of quaternary glaciation when sea levels were much lower. Analysis of stalactites found in the Great Blue Hole shows that formation took place 153,000; 66,000; 60,000; and 15,000 years ago. As the ocean began to rise again, the cave was flooded. The Great Blue Hole is a part of the larger Belize Barrier Reef Reserve System, a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization (UNESCO).
Trevellas
The area towards Trevellas Porth is known as "Blue Hills" due to bluish in-ground slate. Trevellas valley has been a site for tin mining for several centuries, and in 1810 the Blue Hills Sett incorporated many of the small mines. Though Blue Hills closed in 1897, tin production has continued in Trevellas to the present and the Blue Hills works can be visited between April and October each year.