A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

This little brick tunnel built by Confederate forces was used to conduct surprise attacks on the railroad.

This pre-Revolutionary War grist mill ground corn and flour for soldiers in seven American wars.

The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

The skeletal white beams stand as a monument to religious dissent.

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

Ship skeletons haunt Baltimore's waterways.

The world's longest known cave system.

A rock outcropping left by a glacier that made itself useful throughout the centuries.

Since 1947, this living history museum has been providing an immersive look at life in Plymouth Colony.

Supposed Massachusetts Grave of a pre-Columbus Knight Templar.

Featuring the the longest lift span of any vertical-lift bridge in the world.

New Jersey's last historic covered bridge was rebuilt from pieces of the original 19th-century structure.

Where the embers of the Big Bang were first detected.

Rusting away on the edge of New Jersey are the remains of a Cold War missile launch site.

A historic grist mill and active sluice on the Black River.

This tiny structure was built by the creator of the Brooklyn Bridge.

Once in a state of dilapidation, this candy-inspired fortress is now being revived.

The only surviving fragment of the lost Narragansett Pier Casino.

An abandoned Victorian-era mill in the middle of modern Manchester.

This roadside wonder is as mysterious as it is beloved.

This small-town pizzeria won the Hollywood lottery.

Yale University's home for rare works, including the mysterious Voynich Manuscript.

Abandoned Italianate architecture on the coast of Maine.