Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

An ultra-modern vista that has been featured in so many films the house is a celebrity in its own right.

NASA's leading space science lab started by a co-founder with deep ties to the occult.

Hiding amid the largest camellia collection in the country lies a charming children's maze, donated by a secret admirer.

Bug-devouring flora are the stars of a special wing of the glass conservatory.

This ultra-modern home clings to the slope of the Hollywood Hills on a precarious stilt.

This Hollywood dive houses a mural painted by the artists who animated its namesake film.

A spiritual retreat in the heart of Los Angeles offers stunning gardens and a labyrinth to lose yourself in.

The final resting place of a space program monolith.

The illuminating collection of L.A. street lights is run by the city and only opens one day per month.

Long-abandoned art nouveau baths beneath Milan's Piazza Oberdan.

One of Europe's largest supercomputers is housed inside of a disused chapel.

This stunning iron gate designed by Modernist architect Antoni Gaudí is filled with mythic symbolism.

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

For one day every month Barcelona's Estació de França transforms into a market for model trains.

This mansion oasis contains gardens, sculptures, and fountains just off the busy Plaça Kennedy in Sant Gervasi.

This generously endowed statue once stood guard outside a Roman home.

Barcelona's only remaining tram system takes riders to the Tibidabo funicular.

A stately palace has been converted into the world's largest cannabis museum.

Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

A temple to modernity, tucked away amid Barcelona's more well known museums.

An eclectic collection of thousands of items owned by the sculptor Frederic Marès.