565 acres Fort Monroe National Monument was originally explored in 1607 and is the largest stone fort built in the United States. It is a barrier spit of land, with water on all three sides, and has 8 miles of of waterfront and 3 miles of beaches. Which makes it a great area for running!
There are lots of route options here. We’ve mapped out a waterfront route, which runs for 3.3 miles one-way through the National Monument to the end, near Old Point Comfort. The Gulick Dr. section of the waterfront path is 2.8 miles. A great add-on is the ~1 mile road around Fort Monroe. In all, one could do a pretty extensive 8-10 mile in here. There are facilities, and beaches with lifeguards. The beaches are good for running too, but not that long/continuous and the sand is not always ideal.