The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

This knockout museum lies in a sleepy corner of London.

Built on a medieval synagogue, this church has a burial crypt, tunnel system, and Jewish ritual bath hiding deep underneath.

This fantastic cave remained unexplored until 1948 when three schoolboys discovered a hidden entrance.

The United Kingdom's smallest working cathedral also serves as a quaint bed and breakfast.

This skeletal, unfinished Gothic church once housed a miraculous masterpiece by Raphael.

About as hidden as can be, this specialty coffee shop is wedged between multi-story buildings at the end of a dark, skinny alleyway in Seoul.

This beautiful fountain was sculpted by a female artist who was ahead of her time.

Eritrea's futuristic gas station is a nod to Italy's fascist history.

Crop circles inspired this whimsical garden in Germany.

The home of an eccentric Edwardian gentleman is packed to the rafters with handcrafted items collected over a lifetime.

A homemade anatomical collection of medical anomalies and accidental catastrophes.

These small sculptures pay homage to the lovable star of an iconic Argentine comic strip.

A surprising and unconventional mosque hidden in the subsoil of Istanbul.

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

This spectacular bridge supported by two gigantic hands looks like something out of a fantasy universe.

A spiritual sanctuary in a natural cave.

This abandoned Brutalist treehouse is a hidden architectural relic.

Stockholm's deepest subway station is also a stunning ecological wonder.

A mesmerizing sculpture marks the site where the activist was arrested after evading capture for 17 months.

A familiar otherworldly creature guards this 12th-century Scottish abbey.

The roof of this ancient mausoleum is made from a single Istrian stone weighing a massive 230 tons.

Grotto replete with mystical designs laid out in glued shell mosaics.

This cheeky statue of a man defecating gold coins graces the facade of a medieval guildhall.