These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

These caves secretly held national treasures during World War II.

This gem is often wrongly overshadowed by the larger, newer Metropolis church in Athens.

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

Legend says this sacred tree was a gift from goddess Athena.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

A modern sliver of architecture in Roma.

These powerful, if squat, Canadian waterfalls flow in different directions depending on the time of day.

The world's longest covered bridge is a quaint and incredible wooden tunnel.

A mysterious spot where the laws of gravity seem not to apply.

Iconic rock formations that allow for exploration during high or low tide.

This engineering marvel is the longest bridge in Canada and one of the longest spans in the world.

Three buildings constructed of over 25,000 multicolored glass bottles.

Go inside the house that inspired L. M. Montgomery to create one of literature's most beloved heroines.

Rusty red sands line the shores of this Canadian Province.

Possibly the world's largest coin stands just outside of a Canadian science center.

The mastermind behind this palatial hotel perished on the Titanic weeks before its grand opening.

This inexpensive lodging house was once a prison notorious for its inhumane practices.

Louise Bourgeois' 30-foot-tall steel spider sculpture.

A beacon atop a downtown building provides Bostonians with weather forecasts and baseball news.

Millions of numbers carved in glass represent the tattoos forced upon victims.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

This monument on Breed's Hill proves that one of the most famous battles of the Revolutionary War is misnamed.