This vast, water-filled underground labyrinth can only be toured by boat.

Putrefaction plateaus in Iran, where the dead were sent for decontamination before going to their final resting place.

A spectacular rainbow of stained glass makes the "Pink Mosque" one of the most beautiful in Iran.

Iran's colorful terraces are a rare geological masterpiece.

Mirrors and glass shards cover every inch of this arrestingly beautiful mosque.

Legends of time travel and magical woodland creatures bolster the natural charm of this verdant sanctuary in the midst of Moscow.

Stunning examples of Russia's 18th-century wooden architecture.

It's hard to believe the dizzying patterns covering this abandoned mine are completely natural.

A huge Soviet-era robotics factory in the outskirts of Pripyat, now long-abandoned.

Built in the Soviet era, this cableway system still runs gondolas from Odessa down to Otrada Beach.

A century-old church is now a space museum with a treasure trove of Soviet space items.

The largest park in Lviv is surrounded by a network of disused rail tracks.

Marvel at the excessive luxury of the ousted Ukrainian president's former estate.

This hidden fortress has been coined the "City of Ghosts."

Remains of a station that only operated for one year.

A fortress built to pacify local uprising that had a stint as a Nazi concentration camp before becoming a five-star hotel.

It's the only museum of its kind in Ukraine.

The dining hall that nourishes workers in Chernobyl's Exclusion Zone is also open to visitors.

One of the most valuable palace-garden complexes in the eastern borderlands—and one of the most haunted.

The largest catacomb system in the world.

Get past the gatekeeper's apartment and enter an elaborate hoax of a restaurant with a Masonic feel.

This unassuming museum's slogan translates to “there is a limit of sadness, anxiety has no limits."

This beautiful natural train tunnel is said to grant the wishes of visiting lovebirds.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.