Nestled inside the caldera of the Santa Margarida Volcano in northeastern Spain sits something completely uncanny. Since the Middle Ages, the volcano’s crater has been home to Santa Margarida de Sacot, a chapel built by the Catholic Church. Over the years the chapel has become an important pilgrimage site not only for its religious significance, but also for its sheer peculiarity.

Not much is known about its origins (the original chapel’s first written mention occurred in 1403 when Bernat de Ça Terrada, the church’s rector, included it in his will). But what we do know, says Martí Collelldevall, Santa Pau village culture councilor and a member of the committee responsible for maintaining the chapel, is that the church often sits unused, except for maybe once a year during alpec, a religious event that includes a mass, concert, food and live music. The event coincides with the feast of Saint Margaret of Antioch, which takes place every year on July 20.

It’s during these festivities that, historically, hundreds of people have made the 25-minute trek on foot up the side of the 2,238-foot-tall volcano to the chapel, a stone Romanesque-style structure with a single nave and a steeple bell. Built in 1865, the current chapel replaces the original structure, which, interestingly was not destroyed during a volcanic eruption, as the volcano is dormant, but rather in an earthquake sometime between 1427 and 1428. (The volcano, which is part of La Garrotxa Volcanic Zone, experienced its last eruption approximately 10,000 years ago.)

However, preparing the chapel for the alpec has proven to be a logistical nightmare over the years, with volunteers using 4x4 vehicles to lug generators and other equipment up the volcano. Volunteers must also remove vegetation overgrowth that accumulates with each passing month that the timeworn building remains unoccupied. This year, and in the previous two years, the event has not taken place.

It begs the question: Why was a chapel built in a volcano in the first place? And, rather, why wasn’t a chapel built in the nearby village of Santa Pau instead? Wouldn't that have been much easier to do?

Collelldevall says no one knows for sure why the builders constructed it in such an outlandish location in the first place; however, she points to Josep Maria Mallarach, a researcher based in the country’s Catalonia region, where the Santa Margarida Volcano is located, as someone who might have a clue as to why.

“He found a relationship between volcanoes and the Christian symbolism of fire, that has two opposite meanings,” says Collelldevall. “On the one hand, fire is related to hell and evil, but it is also connected to a sacred sense. According to the Christian tradition, Saint Margaret [of Antioch] defeated a dragon, so it is believed that the [chapel] was built in the volcano to protect the inhabitants from fire.”

As with many things in life, perhaps it's best that the idea behind Santa Margarida de Sacot remains a mystery.