Madrid is a gorgeous city in the fall. Bathed in sun, kissed by the breeze, each plaza and terrace is brimming with people conversing their way through a never-ending stream of cañas y tapas–it’s a civilized place, day and night. The Plaza Mayor has been one of its most beloved symbols since the large, stone-paved public square was built 400 years ago. This week, it got a really cool makeover.

Created by the anonymous madrileño artist SpY, the installation is called Césped, or Grass. It transforms the plaza’s granite pavement into a fresh autumn playground, designed to create a memorable experience on the plaza’s 400-year anniversary. According to the information plaque installed in the plaza, the decontextualization of the space will immediately surprise visitors–and, as one of the city’s inhabitants, I agree. It’s shocking to see people sunbathing in this place.

The installation uses more than 32,000 square feet of live grass to lay down a perfect 230-foot-wide circle in the middle of the square, centered around the equestrian statue of Philip III by Flemish sculptor Giambologna in 1616. Philip III was the king who built the original Plaza Mayor in the beginning of the 17th century, following the command of his father Philip II. The latter wanted to turn Madrid’s chaotic junction of streets into something orderly and pleasant for the people of the Spanish capital. The square has gone through several phases over the centuries–including being used by the Inquisition general tribunal in massive judgments against infidels and heretics–until it was destroyed by a massive fire. It was rebuilt in 1790 by the famous architect Juan de Villanueva, who also designed the Prado Museum and the Royal Observatory.

It would be very cool to see other cities changing some of their iconic spaces in the same way, letting people stop and breathe on a patch of green grass. If by any chance you’re visiting Madrid, go as soon as possible. It will only be there until October 1.