33. Manassas Battlefield National Park

Manassas National Battlefield Park preserves the sites of the First and Second Battles of Manassas and associated monuments nestled in about eight square miles (m0re than 5,000 acres) of grasslands, forests, ponds and streams. It has more than 40 miles of hiking trails. The park has recently been selected as an Audubon Important Bird Area.

Trail map. 

Interactive Hiking and BridleTrail Map (requires Google Earth).

One of many interesting trails: the Unfinished Railroad Loop Trail follows an old railroad grade, built between 1854 and 1858, that crosses the park between Sudley Road at the north end of the park and the Brawner Farm on the western edge, and then extends further west across Conway Robinson Memorial State Forest. The planned 35-mile railroad line started in Alexandria, ran through the City of Fairfax to Chantilly, crossed Bull Run at Sudley Springs, then headed southwest across what is now this National Park and Conway Robinson Memorial State Forest, to join the Manassas Gap Railroad in Gainesville, which extended west from Manassas to the Shenandoah Valley. 

Because of mounting costs for purchasing land and moving earth for the track bed, as well as social and economic turbulence during the years leading-up to the Civil War, work stopped  on the rail line one year before it was completed. The steel rails were staged in Alexandria, but none were ever laid on the track bed. It's remarkable that stone was quarried for bridge abutments and all the cuts and fills were done by hand, mostly by local laborers, many of which were slaves and Irish immigrants. Some of the cuts and embankments were used for cover and movements by Confederate and Union troops during pitched Civil War battles. You can tour these battle sites on the "Unfinished Railroad Loop Trail." The rail bed was abandoned after the Civil War.