One of the largest ossuaries in Spain is packed from floor to ceiling with bones.

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

A completely underwater art museum sends a stark message about humans' impact on the environment.

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

A landscape decorated with enormous skull sculptures.

A Spanish forest is filled with mysterious stone carvings.

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

Abandoned for decades, trains still pass through the now-restored remains of one of Madrid's first metro stations.

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

An unusual stroll through gentlemen's erotica demonstrates that pornography is timeless.