An abandoned fort turned state park, Fort Wetherill State Park is a unique mix of history, urban exploration, and scenic views of the ocean and Narragansett Bay. This is also a great place for fishing, boating, and scuba diving. The fort dates to 1895 and was in use until the end of WWII, and there was a previous fort at the same site used during the Revolutionary War. This is a fantastic place for an adventure or just to take in the scenery.
If you go:
There are no entrance fees. Be careful inside the old fort, there is a lot of debris and trash found scattered about the rooms and passageways. Jamestown offers a variety of hotels, Bed and Breakfasts and dining options.
Links:

3 Fort Wetherill Road
Jamestown, Rhode Island 02835 USA
Mailing address:
1095 Ives Road
Warwick, Rhode Island 02818 USA
Phone Numbers:
Fort Wetherill State Park
+1 (401) 423-1771
+1 (401) 423-1771