The Tunnel Hill State Trail is one of the top attractions in Southern Illinois for outdoors enthusiasts. The trail is 45 miles in length and has a nice surface for biking, jogging, or leisurely walking. A couple of the highlights on the trail include passing through an old railroad tunnel and access to the Cache River State Natural Area ( a very neat swampy area containing several state champion trees). If you get to the trail early enough, the trees will provide you shade which can make it pleasant even in the Southern Illinois heat. We passed a few other people either walking or on bikes, but overall, the trail is not very crowded.