Be sure to visit the park in the late summer to catch the blooming lotus and water lilies.
Both the fort and surrounding park are beautiful spaces to explore. Many locals don't realize the fort even exists (which is surprising given the size of the structure) and I've never run into large crowds.
When I was staying in Eagle Rock I was told to visit Roaring Run and I'm glad I did! It's a quick hike but definitely worth a stop. An easy trail follows Roaring Run upstream past multiple waterfalls and small rapids and crisscrosses the river several times over small bridges. Once you reach the waterfall at the end of the trail you can take the upper loop back to the parking lot through the forest and past the 19th century iron furnace. I highly recommend visiting in the fall to catch the changing leaves.