Apparently you're supposed to distract yourself from negative emotions and ruminate on positive emotions. Not very useful if you don't have any positive emotions to ruminate on.
I constantly ruminate on the times my family went to Disneyland when I was growing up. It just makes me sad that it was so long ago and likely won't be the same if I go now :(
Another strategy is to make it a goal to find out. Plan a trip there and let yourself get excited about the possibility of it being just as fun. Chances are, it'll probably be fun, just in a different way than it was growing up.