Built in 1869, the Bollman Iron Truss Bridge, spanning the Little Patuxent River, is the sole surviving example of the bridging system invented, 1850, by Wendel Bollman, a Baltimore engineer. It was the first system, entirely of iron, used by the Baltimore and Ohio Railroad and was the first in America. The company built about 100 such bridges through 1873.
In 1966, under a new program of the American Society of Civil Engineers, it was designated the first ever Historic Civil Engineering Landmark. The bridge was listed on the National Historic Landmark on December 18, 1972, and was designated a National Register of Historic Places on February 16, 2000.
When I was in middle school, I lived nearby and used to enjoy exploring the bridge, nearby ruins, and the river. I hope you enjoy the site, as well.
From the posted coordinates, you will find some plaques. You need to find a four digit number on a blue background. This will serve as the LOG PASSWORD. You must also post a picture of yourself and/or your GPS with the bridge.