Fort Mifflin is a National Historic Landmark overlooking the Delaware River by the Philadelphia airport. It is one of the few American forts still standing that existed before 1776. On our tour, we learned it was a fort built by the British, and then captured by Revolutionary patriots. Fort Mifflin’s 200 heroic soldiers played a critical role in holding off the British “to the last extremity” so that Washington’s troops could winter in Valley Forge.
The costumed interpretive guides were great at answering our questions.
You can wander the grounds and enjoy river views by walking along the wall. The park is dog-friendly, there’s free onsite parking and a wild naure trail loop that follows the river. Amazingly, it doesn’t received Natrional Park funding, relying on volunteers and generous PA organizations. 
Fort Mifflin rates in the top 10 most haunted places in America. There were many soldiers, prisoners of war and family members who died here, often under gruesome circumstances. Paranormal investigators and Fort staff have recorded lots of otherworldly sights and sounds. Fort Mifflin is a popular destination for spooky overnight scout sleepovers.
We noticed that some of our night visit photos caught flickering lights. In my Casemate 5 wall photo, I swear there’s an image of a face on the wall.