The ceiling of Prohodna Cave in northern Bulgaria affords a peek at the sky via two deity-sized-eye-shaped holes.

These cascading falls resonate throughout the Bulgarian forest.

A massive cave once a secret military base is now home to thousands of bats.

Böttcherstraße's bells, extolling Nordic virtues and the great conquerors of the world.

A spitting ode to a German serial killer.

A stunning gilt bronze relief denounced by Hitler as "degenerate art"—even though it was dedicated to the Nazi leader.

One room inside this building mesmerizes all with its parabolic dome.

The only microgravity tower in Europe can produce nine seconds of weightlessness.

Constructed by forced laborers, this submarine pen is now a museum and war memorial.

A Nazi concentration camp and Anne Frank's place of death.

A fire once nearly devoured this gorgeous 14th-century Gothic cathedral.

This snug medieval lane is one of the narrowest streets in the world.

The European towns of Brașov and Râșnov each have proud signs reminiscent of the Hollywood sign.

The possible imprisonment of Vlad the Impaler here earned the medieval castle its nickname, "Dracula's Castle."

Climbing to the top of the cathedral's bell tower offers sweeping views of these medieval ruins.

This elaborately decorated, fairytale-like Romanian royal palace is one of the most striking castles in Europe.

This enormous abandoned prison was once dubbed the "Bastille of Romania."

This eccentric folly house was designed by Romanian thinker Bogdan-Petriceicu Hasdeu, with a helping hand from his deceased daughter's spirit.

A muddy alien landscape that is home to rare species of exotic plants.

This memorial to the victims of the Romanian Revolution of 1989 is often compared to a potato on a skewer.

Check out engineering marvels of the past at this unintentionally retrofuturist museum.

This solitary monastery may hold the remains of Vlad the Impaler (but probably not).

17th century palace once a meeting place for politicians.

After sitting unused for decades, this abandoned communist infrastructure became a wildlife utopia.