What a huge stack of wriggling arms and legs! It’s a tower made of humans. Or, as the Spanish like to call it, a castell.

A castell-building contest happens every year in Catalonia, Spain. First, a bunch of people meet in a square. They start standing on each other’s shoulders and heads every which way. After a little while, voila! You have a tower!

Wait, rewind. It isn’t that easy. Really members of human towers practice for months. Their tower has a precise form. The larger people at the base of the tower act as a mattress in case the smaller people near the top make a misstep and fall. It is tense work. People watching probably bite their nails!

The contest is supposed to display strength, balance, and courage—and show off Catalonia to the whole world. It’s not a bad idea. Wouldn’t a 10-story people-stack get your attention?