Nurse Falls for Quirky Asylum Patient Comedy

Saw this movie one time where there was a quirky mental patient who did funny things. Happy guy. He had a small underground bunker / fort where he would retreat to. He falls in love with a nurse and in the end she falls for him and the question arises whether he is really insane or not.

I believe this was an older movie. Maybe even black and white??

Anybody?

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Strange – that could be a misremembered version of The Fisher King in a way.