An underground network of massive stone arches and their skylit vaults support ruins of portico structures above.

An homage to the medieval rulers of Bulgaria.

An unfinished complex built for children from around the world sits abandoned on the Black Sea coastline.

A mountain pass in Bulgaria's Balkan Mountains was the site of four historic battles.

This once-grandiose behemoth of a monument from the socialist era now sits quiet and closed up.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

The site of many battles and tragedies, including the 40 maidens who leapt into the sea.

A spectacular Bulgarian cave resembling a devil's head with a waterfall rushing down its throat.

This historic black and white monastery is one of Bulgaria's architectural jewels.

A building that survived WWII, possibly on the virtue of its name alone.

The bronze uniforms commemorate the vital role of women during World War II.

This medieval church tower has maintained its clockworks since the 16th century.

Sculptor Antony Gormley used chaos theory and fractal growth to design his tallest creation.

London's only public statue of the much-married monarch adorns the gate to St Bartholomew’s Hospital.

This marine reptile was discovered by one of the 19th century's greatest fossil hunters.

Hackney's newest private museum and natural curiosity shop.

A tiny replica of the iconic London landmark hides on the side of the steel structure.

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

Since 1887, this old-school shop has stacked its shelves with extraordinary coffees and teas.

The wooden telephone box hidden away in London's Piccadilly was the original prototype of the iconic kiosk.

This one has sailed five times as far as Sir Francis Drake's famous ship.

A memorial to a dog that inspired rioting in the streets of London.

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

The rose garden in Regent's Park where Pongo and Perdita met for the first time in Disney's "101 Dalmatians."