Even many of South Dakota’s most avid travelers haven’t stumbled on Jewel Cave because, frankly, it’s the last stop going west on Highway 16 — and who wants to leave South Dakota? But drive just 13 miles west of Custer and you’ll experience a canyon and cave country like nothing else in the state. The National Park Service charges modest admission to the cave; the trails and facilities are free. There are three hikes — the short Roof Trail just for a taste of the scenery; the moderate 3.5-mile Canyon Trail; and (a mile west of the cave entrance) the 5-mile Hell Canyon Trail, which descends deep into the limestone canyon. Everyone thought the cave was just a shortie when President Theodore Roosevelt created the park in 1903. By 1959, spelunkers had traced it 2 miles. Now we know it’s over 200 miles long — third-longest in the world — so some wonder if it might possibly be part of the Nebraska Cornhuskers tunnel walk?