1. Klingle Road
Klingle Road was once a street in northwest DC but was closed to traffic in 1991 because it had damage from erosion. There was a large dispute over the road between residents who wanted the road repair and others who wanted to keep the part of Rock Creek Park free of cars and turned into a trail for hikers and bikers. Eventually those in favor of the trail won the dispute and work on the Klingle Trail began in 2015 but you can still see remnants of Klingle Road in Rock Creek Park.
2. Capitol Stones
The historic Capitol Stones are one of DC’s great mysteries. They are completely hidden and not many DC residents know where they are but they are actually in plain sight in Rock Creek Park. These blocks of moss covered marble stones were once a part of the US Capitol. In 1958, the Capitol Building was renovated and parts of the east facade were dismantled and parts of the portico were removed. These stones for whatever reason, were piled up in Rock Creek Park and they have remained for over 50 years. The lure of the stones is that those who have visited do not give away the exact location of them.
3. Aqueduct Bridge Abutment
The Aqueduct Bridge was once a bridge between Georgetown and Arlington that transported cargo-carrying boats on the C&O Canal across the Potomac River. It was closed in 1923 and demolished ten years later. Part of the bridge, the abutment still exists on the west side of the Key Bridge in Georgetown and has become a canvas for graffiti artists.
4. Forest Glen Seminary
Forest Glen Seminary has had many different changes over the last one hundred years. It was once an all-girls finishing school and then was later owned by the Army who used it for a place where wounded soldiers could come to recuperate. They stopped using the property in 1977 but owned it until 2004 and let it fall into disrepair. Today part of the property has been rebuilt as town homes and condos and parts remain as they have been. You can still tour the area with a tour guide or on your own. Just head to 2755 Cassedy Street, Silver Spring, MD 20910.
5. The Patowmack Canal
The Patowmack Canal, conceived by George Washington, was a series of five canals in Maryland and Virginia that were designed to bypass the rapids of the Potomac. The canal was abandoned in 1830. While technically outside of DC, the remnants of the Great Falls portion of the canal still lives in Great Falls park. The area is clearly markted and you can visit the Canal when you visit Great Falls Park
6. Washington & Great Falls Electric Railway Trestle
There’s an old railway trestle being overtaken by leaves and vines near Georgetown. It was once a part of the Washington and Great Falls Electric Railroad, a street car that ran from Georgetown to Cabin John, Maryland in the early 1900s. Now it looks like the trees have grown a bridge in the middle of the forest. You can reach the trestle in the wooded area just off Foxhole Road in Georgetown.