But this wasn't all fun and games: the "First Lego League" is also a lesson in how to solve problems using science and technology.
Students at Mersch's Lycée Ermesinde participated in the global competition on Saturday. Since going back to school, all those aged between 9 and 15 have been putting their thinking caps on, trying to devise what the city of the future should look like.
Aside from building the city, they had to provide scientific research to support their ideas and pass certain tests.
(Video in Luxembourgish)