At 184 miles, the bumpy and beautiful C&O Canal towpath is the region's longest, flattest and most secluded biking and hiking trail. But it is dirt mixed occasionally with crushed and uncrushed rock and lumpy with tree roots _ perfect for your new dirt bike or old heavy- wheeled clunker but sometimes hard on narrow tires. It also is muddy and slippery after rain.

On weekends, especially between Georgetown and Great Falls Tavern (the National Park Service's canal interpretive center), the towpath can be almost impassable with people and difficult to get to by car. But if you start early and come back late, or cycle the path above Great Falls, you may miss the crowds and even find a parking place at one of the locks off River Road.

For cyclists who might want to try an overnight trip, there are eight hiker-biker campgrounds (with water, toilets and grills) along the 60 miles of towpath between Washington and Harpers Ferry, where there is also a youth hostel and a mountainside hotel.

It's also possible, though not necessarily desirable, to pedal the 184 miles from Cumberland to Washington on a three-day weekend. It's all downhill, gradually.

But the towpath is best seen at a leisurely mule's pace, with frequent stops at aqueducts, tunnels, locks and lock houses and watering holes along the canal, such as at White's Ferry, Point of Rocks, Brunswick and especially Harpers Ferry.

Few bicycle clubs schedule group rides along the towpath because of its rough surface, but most experienced cyclists have ridden along it at least once. It's a unique and historic ride back into the 19th century.