Watkins Glen is like nothing else I've seen anywhere in the country. The geology of the area creates layered rock formations through which canyons form. They are very grey and green with lovely cascading waterfalls and rivers. Such gorges can be found all over the Finger Lakes area of Western NY, but Watkins Glen is the gem of the whole area. More waterfalls than you can count! Most trails are fairly well-developed with stone paths and stone stairs but can be very steep.
Only swim/wade and hike where permitted!!! Children and drunk adults seem to drown every summer by swimming in deceptively calm areas that lead to extremely deep and/or swift water. There are also very steep drop-offs if you leave the trail. This is not a dangerous site as long as you follow the rules.
Tons of trails, lots of swimming options, many many other state parks in the area. Camp here for quite a few days and then explore the whole area, including "hippie" college town Ithaca. Exceptionally high quality State Park facilities, including all the usual amenities, plus more like canoe/boat rentals. All kinds of camping options, from tents to cabins. Make sure you reserve in advance! We've camped at lots of different sites over the years and each has been great. Accessible sites are excellent.