Entertainment that caters to those who brains are fully formed. Thoughtful, slow, academic activities. Museums, classical music, eating salads
There's nothing wrong with a day of escaping your adult responsibilities and indulging your childhood desires, but doing so without a child accompanying you is strange.
As a kid, I liked going to Chuck E. Cheese and playing the Star Wars arcade cabinet game. If I went to Chuck E. Cheese as a grown man without a child, I would be shamed, and rightly so. The same goes for Disneyland