As an adult, what seemingly childish things do you get excited about?
I love bridges. If I see a cool looking bridge, I want to cross it, especially if it goes somewhere that I'm not familiar with. Same with stairs outdoors. They feel like an adventure to me.
Metro. Train go underground, yay! Probably helps that where I'm from they're pretty tidy.
Mechanical items being repaired. It didn't work as it was supposed to, now it does, magical, you healed it! (Sometimes it's even me being the magician.)