Blue Hole (Castalia)
The Blue Hole is a fresh water pond located in Castalia, Erie County, Ohio, in the United States. From the 1920s to 1990 the Blue Hole was a tourist site, attracting 165,000 visitors annually at the height of its popularity, partly because of its location on State Route 269, about southwest of the Cedar Point amusement park in Sandusky, Ohio.
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.