The meme that others have done, using this Great Circle Mapper.
Here are the flights inside the US:
And here are those inside Europe:
The flights in the US contain a few routes I'm not sure about: when my sister and I were the States years ago for a family reunion, we got a 30-day pass enabling us to fly stand-by on Delta and its partners as much as we wanted, and we visited quite a few places (mostly staying with friends or acquaintances of my mother's). While I think I've got all the airports we flew to during that time down, I'm not quite sure of the order in which we visited people; the above is my best guess/recollection.