Every two years in early October a crazy event is held in Spain – and the good news is, it’s on again in 2018.

It’s called the Concurs de Castells de Tarragona and is basically a gigantic human towers competition.

It takes place in the beautiful town of Tarragona, about 100km outside of Barcelona. Teams compete to build complex human castles (called castells), many tiers high – the record is 10.

But that’s just the towers – they’re supported by teams of up to 500 men, women and children who gather in the middle of the arena dressed in their respective – and bright – colours.

These castellers create the base of the tower first. Then members climb up the sides of their teammates and stand on their shoulders to form each layer.

Read more: Spain is a feast for the 60-year-old senses

Read more: 7 brilliant things to do in Barcelona

Next, a child climbs to the summit and raises their hand to indicate that the tower is complete. (Don’t worry, they wear special helmets designed so that they protect the child’s head, but are also soft on the outside so that, if the child should fall, they won’t harm anyone else on the way down.)

Finally, the towers are dismantled layer by layer, from the top down. This can be the most dangerous bit of the whole process, and a castell is only considered a success if it’s built and unbuilt without falling apart.

Teams have five rounds in which to build towers. It may look like a big free-for-all, but points are scored based on the difficulty and height of the tower built. The best three towers count towards the final score, and the team with the highest score wins.

The event, which dates back to the end of the 18th century, has been declared part of the List of Intangible Cultural Heritage, established by UNESCO. It’s so exciting, and so popular with locals and tourists alike, that more than 20,000 people come to watch!