Take a Walk
Stepping away from life and going for a walk (without added stimulus) helps your brain engage topics more effectively. Removing yourself from a situation and thinking about it from another angle helps you change your perspective. Thinking around a problem instead of trying to think through it will make you better equipped to solve problems in the long run.
Visit a Museum
Museums are still extremely popular for a good reason! Visiting a museum doesn't make you inherently more intelligent, but if you go into the museum with a clear goal in mind, you're likely going to walk away with some beneficial information. Even if you just want to go to a museum to learn about something new or find inspiration in what you've been doing, you're still gaining knowledge that you didn't have before.