One of the foremost Sherlock Holmes collections is hidden away at a Toronto library.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

Mausoleum and Holy Seat of Antiochus I of Commagene.

The largest Neolithic ruins in the world hide a notably clean prehistoric metropolis.

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

Once described as the "Eagle's Nest," this ruined ancient city rests on a remote mountaintop.

Live a night as a Byzantine King, with a minibar and private jacuzzi.

Naturally protected city carved from a rock face.

An abused and forgotten metropolis, abandoned for centuries.

A Lycian city of the dead carved into the hillside of Southern Turkey, complete with startlingly human touches.

A deadly ancient portal to the underworld.

This famous city eluded concrete detection until the early 2000's.

This hunter-gatherer architecture is believed to be the oldest religious complex known.

These tombs were built into the side of a mountain so that ancient angels could reach the dead.

Roman ruins top white travertine terraces formed by ancient hot springs.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

Macabre astrological automaton clock dating to the late 1400s.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.

This artificial cave looks like something out of a fairytale.

Walk through Czech history in Prague's largest graveyard.

A museum of alchemy and a basement laboratory all housed in an ancient building in a Gothic tower.

A church of bones, decorated with 40,000 human skeletons.