We've lived in the Downingtown area almost four years (West Chester before that) and passed by a number of times, saying to ourselves that we have to visit. So we finally did and it didn't disappoint.
We only saw a small portion of the 900+ acres of the area where you can hike, take a walking tour in and around the historic iron workers (and later Philly lawyer's) 'mansion', kayak, or fish on the lakes and in the Brandywine Creek.
There's also a pavilion for some outdoor performances, vast grass fields, playground, and camping grounds. Some of the hiking trails (might as well be service roads) lead to great spots with handicapped parking and beautiful views of the lake.
The wooded areas are luscious and full of bird watching opportunities, or just connecting with nature and finding yourself and inner peace.
We had great luck witnessing a power play between three or four vultures that found a dead fish by the dam and one very brave crane (or heron?), which was hilariously interrupted by two geese that were just observing the whole thing from a safe distance before.
There's no way we won't be back. Looking forward to it!