National Park Facts

The Lincoln Memorial has a secret: a 43,800 sq ft cave beneath it - nearly twice the floor space of the memorial above. Rainwater seeping through the marble has grown real stalactites, and 1914 construction workers left cartoon graffiti on the columns, now preserved behind plexiglass. It opens as a public museum for the first time on June 25.

The Lincoln Memorial hid a secret room for over 100 years. It just opened to the public for the first time. The new $69 million museum has floor-to-ceiling glass walls. Visitors can walk past the columns holding up the memorial above. Lincoln's own signed Emancipation Proclamation and 13th Amendment are inside.