There’s a lot to see in the streets of Barcelona. But what about the secrets beneath them? Atlas Obscura traveler Nanci Courtney shares a moment fromBarcelona Behind the Scenes: Cabaret and Carnival.

At the University of Barcelona, our group entered a beautiful mansion that now houses the school’s administrative office. Felipe, our guide, spoke with the security guard. The two of them led us to the lower floor, where they unlocked several doors. Behind them, hidden away, was a secret tunnel.

Felipe told us the tunnel was dug by hand in 1936, during the Spanish Civil War, when Barcelona suffered terrible airstrikes and bombings. The government used the mansion above (the Palau de les Heures) as a secret retreat for the Catalan president, Lluís Companys. As for the bomb shelter below, most of the people who work in the building today have no idea it’s there.

We put on helmets and entered the tunnel. It was seriously cramped! There wasn’t much air, so it's not OSHA approved, which makes it all the better! But I practiced mindful breathing. The tunnel was a truly unique experience, because Felipe had to get a special permit for us to visit it. Wow! It was an incredible trip down a rabbit hole.