The Cerro de las Campanas (Hill of Bells) is known as the place where Emperor Maximilian of Habsburg was shot. Those who visit look for the site of his death, many unaware of the meaning behind the park's name. 

The name of the hill comes from the phonolite, a strange and unusual type of volcanic stone with low silica content. When you hit the stone, it produces a metallic clink. As such, the rock is named for an Ancient Greek word that means "sounding stone." As the park is home to these ringing rocks, it was named the Hill of Bells.

When visiting the park, you'll find a a series of stones distributed around the hill. These scattered stones form a puzzle-like experiment for visitors. Only one of the rocks is phonolite, meaning you'll have to tap a fair amount of ordinary specimens before finding the one that rings.

Sadly, a lot of the phonolites disappeared because of sticky-handed visitors. Only the largest specimens remain. The rare rocks are so treasured they're protected, and have been declared state property.