The German phrase ‘Luftschlösser bauen’ literally translates as ‘building castles in the air,’ a whimsical image indicative of the idiom’s meaning — daydreaming about pipedreams.

(SOURCE) https://www.cnn.com/2022/05/13/football/jurgen-klopp-marco-reus-dortmund-liverpool-spt-intl/index.html