A favorite haunt of dinosaur loving children and hallucinogen loving hippies alike.

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

A 140-year-old castle with underground caves hidden in San Francisco.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

Formerly known as Saville Theatre, this mid-20th-century entertainment hub includes an ornate frieze.

This toxic spoil heap found a second life as a ski slope, popular film location, and wildlife haven.

This ancient oak plays host to carvings of magical elves, gnomes, witches, and other creatures prominent in local folklore.

This peeling mural of Adam and Eve was inspired by the greenhouses at Kew Gardens.

London's most popular recording studio, located in the capital's East End, runs partly on solar power and has played host to some of the world's biggest acts.

This secret garden has bloomed into London's most unique hub of urban creativity.

The broken skateboards that became a poignant memorial to a murdered skater.

Black cat statues guard this temple-like Egyptian revival factory.

Where condemned pirates met their grisly end at the gallows on the River Thames.

A relic of Victorian grandeur hides beneath a busy South London road.

This secluded walkway overlooks a magnificently wild London green space.

A network of concealed passageways lies within a busy London Underground station.

The remains of Crystal Palace Great Exhibition of 1851.

An alleyway plaque is all that remains of the independent Texas' envoy that forgot to pay their rent for over a century.

The final resting place to 300 Victorian-era pets hides inside the city park.

Remnants of a Victorian garden feature sitting in public woodland.

Rebuilt remains of a temple to Roman god Mithras.

A vast overgrown cemetery, once known as one of London's "Magnificent Seven."

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.