The site here is Leathrman's cave -- a place that the Leatherman stayed on his circular routes. To reach the cave, follow the Mattatuck Trail out of Black Rock State Park.  

Leatherman (vagabond)

The Leatherman (ca. 1839–1889) was a particular vagabond, famous for his handmade leather suit of clothes, who traveled a circuit between the Connecticut River and the Hudson River, roughly from 1856 to 1889. Of unknown origin, he was thought to be French-Canadian, or simply French, because of his fluency in the French language, his "broken English", and the French-language prayer book found on his person after his death. His identity remains unknown, and controversial. He walked a 365-mile route (taking 34-36 days) in western Connecticut and eastern New York.

• http://en.wikipedia.org/wiki/Leatherman (vagabond)