I would never go to an amusement park without kids, that's for sure. I am not crazy about amusement parks. I hate big entrance fees, lines, costumed characters, parking lot trams, the whole contrived fun experience. I don't like turnstiles. Usually, I like to watch people but people-watching at amusement parks is generally unpleasant. I do like getting my hand stamped, though, especially with the ink that only shows up under a black light.
Plays and concerts are more fun with kids, as long as they're not being bratty. It's difficult, though, to predict when they'll be bratty. That's the problem with shopping, too--I'd rather go to the grocery store with kids than without, but I don't want to go anywhere with whiny monsters.
I generally play games only with kids. I wonder if camping would be much fun without kids? I'm not eager to find out.
For entertainment with no juvenile companions, I like to watch movies that aren't scary, read books, put fabric-y things together, drink beer. I like bicycling, but it's sort of a chore if I'm not alone.