A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

The haunting "Hell House Altar" is one of the few remnants of an abandoned college that has been a magnet for local legends.

An eerie, decaying ghost town destined to fade into the forest.

The shelves in the back of this thrift store are devoted to saving, not selling, retro tech.

This library is designed to commemorate the work of the Human Genome Project.

She stares out across six lanes of traffic, clutching a musket and infant with determination.

The headquarters of the Audubon Naturalist Society is a small slice of heaven for nature lovers.

An astounding collection of medical specimens, including bits of President Lincoln.

Hidden within an idyllic suburban garden is a memorial dedicated to the victims of a terrifying spree of killings committed on U.S. soil.

This four-story steel sphere in Maryland was used to test biological weapons.

This hidden treasure provides a charming access point along the south side of Baker Park.

A Civil War Museum with some notable medical antiques.

The hidden ruins of a mill that is linked to an attempt to assassinate the vice president of the United States.

This ruined quarry once produced the distinctive red sandstone used for construction projects in Washington, D.C.

Three abandoned missile silos are hiding in plain sight behind a suburban development in Maryland.