Well, I'll have to go with Cuyahoga Valley National Park. It begins south of Cleveland and runs along the Cuyahoga almost to Akron. Accessibility--it has to be number 1. I-80 actually runs over the park. (OK, that could be a negative). It's narrow in some places, but it has the river and in places the canal that ran beside the river. Lots of birds. It's a great place for warblers in migration season with some who stay for the summer. There is a trail that run along the canal that is wide and flat. There also are other trails that can be fairly steep and there are mountain biking trails. Tons of lodging near the park. It's a great amenity for northeastern Ohio. But frankly unless I were collecting national parks, there isn't a reason to visit.