Route: Mammoth Cave Railroad Bike and Hike Trail (KY)

At the northern end of the Mammoth Cave Railroad Bike & Hike Trail is the impressive Mammoth Cave. With 390 miles of passages, it's the world's longest cave, more than double the length of its closest competitor. Named for its massive size (and not woolly mammoth fossils, which have not been found there), the cave is one of the oldest tourist attractions in the country.

The Mammoth Cave Railroad was privately owned by entrepreneurs who also owned lodging along the way. Its railroad ties were put in place during the summer of 1886 and, by that fall, two- and three-car trains were barreling down the corridor. Mail was also carried by the train, and the Chaumont Post Office was included among the many stops during the short, 25-minute journey between Park City and the cave.

Trains continued on the line for more than 40 years before service finally ended, largely pushed out by the rise of the automobile. In 1936, the rails were removed, but one of the last engines, dubbed Hercules for its pulling power, can still be seen today just south of the visitor center for Mammoth Cave National Park. Formally a streetcar, Hercules was converted for use on the narrow-gauge railroad and is shown pulling a train car in the line's hallmark red color.

Today, the pathway provides a scenic, wooded experience, but note that its loose gravel surface is best tackled with mountain bikes or hiking boots. And, unlike most rail-trails, which are relatively flat, this trail has a few hills. Along the route, there are three well-marked areas where the climb is so steep that it's recommended that cyclists dismount and walk up the hill.

The southern end of the trail lies on the outskirts of Park City (known as Glasgow Junction in the railroad's heyday), where you can explore the old stone structure of a stagecoach stop at Bell's Tavern, built in the early 1800s.

The trail is about 8.8 miles one-way, with about 400' of elevation gain