While this certainly does not qualify as an example of fun architecture, this is a great example of people having fun with architecture.
Life Without Buildings speculates that, contrary to the claims of the Star Wars designer that cooked up the plans for Han Solo’s starship, The Millennium Falcon wasn’t inspired by random foodstuff.
However, I’m more inclined to believe he was flipping through the pages of an Otto Wagner book and came across his 1880 design for the central offices of the Vienna Giro und Kassenverein competition.
Raw speculation or brilliant insight?
For me, the question is: Are certain forms naturally fun? Maybe more precisely, any form can be imbibed with a cosmic fantasy.