A faded reminder of what was once a common sight in London during the Blitz.

A lasting remnant of the London Blitz.

One of Madrid's oldest trees, with a long and colorful history, resides in El Retiro Park.

This piece of early engineering is rather unknown despite its location in the heart of Madrid.

One of the best examples of the modernist movement in Madrid.

This lucky bronze frog was gifted to Madrid by a casino.

This royal shrine and cemetery is hidden amidst modern public housing.

A venerated grave atop an ancient royal hill, often attributed to the last king of Singapura.

A statue that would be at home in Rome can instead be found in the heart of Norway's oldest city.

This one-of-its-kind shipyard brings the 12th-century Viking Age back to life.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

An architectural oddity hides in plain sight on this iconic London bridge.

Before becoming a poet John Keats studied here to become a surgeon.

A preserved portion of an ancient Athens barrier is displayed in a hotel basement.

According to legend, this ancient column contains healing properties.

This mystical orb covered in strange symbols is thought to have been used in ancient Greek magical rituals.

These ancient ruins hide in plain sight next to a dessert shop.

The only surviving choragic monument is a trophy awarded in 334 BC for the winning dramatic chorus.

This abandoned shopping arcade has new life as an art installation.

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

Where commuters walk through remnants of an ancient Greek necropolis.

This gem is often wrongly overshadowed by the larger, newer Metropolis church in Athens.

Legend says it was constructed with the destroyed pillar of an ancient Greek Temple.

This open-air mosaic gallery honoring an English artist took hundreds of volunteers more than seven years to create.