Largest Roman Catholic church in North America.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

A nostalgic bibliographic gem.

The walls of the iconic dome are hollow and have a secret stairway.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

North America’s largest collection of horological devices and home to a colossal clock with a dizzying array of features.

This Old Testament garden features 100 plants from biblical times.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

Exact replica of the ancient monument, but much, much lighter.

This bright yellow relic is the final survivor of a short burst of seashell-shaped petrol pumps.

A former Oz-themed attraction that has fallen into disrepair, but still holds some of the original magic.

One of the oldest anatomical theaters in the U.S. still in use was once the site of an infamous cadaver riot.

The design of this historic domed church was influenced by Thomas Jefferson and intended as a statement of religious freedom.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

The trials and tribulations of marking Poe's grave.

A blank headstone topped with a pile of pennies marks the final resting place of the infamous assassin.

This grave marks the passing of a historic Jane Doe whose identity remains a mystery to this day.

America's first federal monument.

A clock designed to run with perfect accuracy for 10,000 years.

Air Force Academy Chapel made of 100 identical tetrahedrons works to inspire those of all religions.

Huge concrete structures designed as an early warning system for Britain to detect enemy aircraft.

The largest university building in the West is a gothic masterpiece containing dozens of theme rooms based on different countries.