Visiting the Sacro Bosco (Italian for Sacred Grove), a 16th-century garden in Bomarzo, Italy, is no ordinary walk through the park. The seven-acre site’s sculpted monsters, open tombs and dramatic depictions of supernatural combatants make the experience more akin to braving a Renaissance version of a haunted house. Visitors can wander through a tilted building, run away from a giant gaping mouth and—if they manage to get past Cerberus, the three-headed dog who guards the gates of the underworld—descend into hell.

The Sacro Bosco’s colossal stone statues are frightening to behold. But what makes this garden extra eerie is that no one knows for sure why monsters haunt these woods. “No receipts, account books or commission documents survive to tell us about the Sacro Bosco’s creation,” says John Garton, an art historian at Clark University and the co-author of an upcoming book about the garden. Pier Francesco Orsini, the duke who commissioned the Sacro Bosco in the mid-1500s, left no explicit clues.