The 41-year-old actor, who will portray Batman in the "Man of Steel" sequel, was so obsessed with his character that he built a replica of the entrance to the secret den where his character Bruce Wayne keeps his alter ego's suit, weapon and vehicles, reports femalefirst.co.uk.
"When I first saw (his house) he was touring me through the place and said, 'Come here, I gotta show you my room'," said director Kevin Smith, a close friend of Affleck.
"He brings me into the room and goes, 'Look at this'. There's an office room and this beautiful bookcase - he reached under and he clicked something and all of a sudden the bookcase opened.
"I was like, 'No! You built a f***ing Batcave?' And he was like, 'No I built a Batcave entrance!' When you went in behind the bookcase it was a panic room," added Smith