It’s Prague’s annual carnival of lights!
These steps play triple duty in the film! The first time they show up are when Peter jumps off the balcony after talking to Mysterio. That moment was shot at the top of the steps with Loretánská Street in the background.
The next time it’s seen as the class is heading off to the (upgraded) opera. This was shot at the bottom of the steps with the Malá Strana dome lit up in the background.
Finally, Peter heads back to his hotel after the fight in the square. This was filmed around the middle of the steps.
(Spider-Man: Far From Home, 2019)