Oh, where to start... The list of eras, places and people to see would be phone-book thick!
However, if I could pick just one destination, I guess my answer would be the same one that my nine-year old self would give: Somewhere with Dinosaurs. Imagine how incredible a sight it would be to witness a Brontosaurus herd roaming the land.
But I'm not picky. Just suprise me and take me anywhere.
As long as it doesn't have Morlocks.