Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

This Navarrese cave's history of witchcraft and pagan ritual is not just embraced, but recreated each year.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

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

A cemetery in Barcelona's Poblenou district is home to this touching funerary statue, which depicts death in the form of a winged skeleton.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

This fascinating and poignant museum chronicles every imaginable aspect of Spanish colonialism in the Americas.

One of the world's oldest universities houses an incredible collection of anatomical models, mummified body parts, and human bones.

The sole surviving relic of the San Francisco neighborhood cobbled together from old horsecars and streetcars.

Adolph Sutro's little-known, geographically inaccurate, deprecated monument.

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

The only visible piece of San Francisco's most famous shipwreck.

Visible below the waves are memorials to the city's Gold Rush dead.

A modern mechanical planetary system, part of a 10,000 year clock.

Centuries of biking history are nestled in the shadow of the birthplace of contemporary mountain biking.

One man's love of natural beauty led to the creation of this hidden granite monument.