This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

Grand Orthodox cathedral with walls filled with frescoes and icons.

A striking symbol of the Bulgarian capital.

Climb a set of vertiginous stone steps to the top of this impressive ancient edifice.

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

The most metal church of all time was built in record time because of an international, pious pissing contest.

A fountain standing as a testament to a doomed alliance.

Ancient serpentine sacrifice holder that has stood the test of time.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

A marvel of Byzantine engineering under the streets of Istanbul.

A historic 1890s architectural masterpiece with an iconic clock tower that, once open to the public, now faces an uncertain future.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

This lovely, if imposing, piece of Canadian gothic is possibly the most photographed hotel in the world.

The "Seinfeld" diner.

This giant boulder is sandwiched between apartment complexes in upper Manhattan.

After surviving abandonment, this powerful Latin American mural is alive again.

The oldest operating apothecary in the US has treated everyone from Thomas Edison to Mark Twain.

An aptly-named street near the birthplace of the modern LGBT rights movement.

An ancient mineral hot spring sits at the middle of this combination cultural center and spa.

At the western edge of Palm Springs, a rugged desert canyon trail leads to a waterfall at the base of the San Jacinto Mountains.

An eerie natural formation that looks right back at you.

This Big Sur waterfall drops 80 feet directly into the Pacific Ocean, and inspired the hillside house up top.