There are a few moments in time that stand out for people: their wedding, birth of a child or, often, a traumatic event. Lots of folks know where they were on 9/11 (I was on a train in Brooklyn and saw the towers burning). But, for a lot of people, the assassination of President Kennedy still triggers the strongest memory.
I'm trying not to make this sound like a vacation recommendation because that's not what I mean (and it's far too ghoulish). But there's something to be said about visiting a place where something important, if terribly tragic, happened.