A tunnel that brings more than a century of history to life from the deepest parts of the Niagara Gorge.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

The world's oldest soul food restaurant is also one of its best.

The hippo that stands on this university campus was once a drunken flea market purchase.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

The National Park Service’s best-kept secret with views that rival any in D.C.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

At this rare mosque in Tbilisi, Sunni and Shia Muslims pray side by side.

A cluster of historic bathhouses built on the famed hot springs that gave the Georgian capital its name.

Railroad officials in the early 1900s sought to spare travelers the sight of Roman soldiers’ private parts.

The record holder for the world’s largest peach.

This bridge over D.C.'s Rock Creek Park is sometimes called the "Buffalo Bridge" because of its four buffalo sculptures, which were cast from a single piece of bronze.

This historic fort spans more the 300 years.

This vessel is believed to be the oldest operating fireboat in the world.

Take an underground boat ride through a former hydraulic raceway that was built in the late 19th century.

A dazzling display of lights and crystals.

Funded by John D. Rockefeller, this is one of the earliest, and most beautiful, shopping arcades in America.

Marvel at this turn-of-the-century masterpiece that has been turned into a rather stately supermarket.

This campus chapel is Robert E. Lee's final resting place and a topic of debate about the legacy of the Civil War.

A 400-foot-tall tall map of Chicago makes this once-ignored building stand out.