It's admirable and healthy to keep up with your fitness goals on vacation, but there's a big difference between running on the hotel gym's treadmill versus going on a daylong running trip, or challenging yourself to a marathon in an international locale. Many travel companies like Run of the World specialize in putting together running vacations to Europe centered around noncompetitive fun runs or world-class marathons, such as the London Marathon or Amsterdam Marathon. It's certainly a unique way to sightsee, running through the streets of major world cities with the traffic blocked off. Running the Athens Marathon is even educational, replicating the historical ancient Olympic experience. And unlike other adventure vacations, you don't need to much additional gear besides running shoes, nor will you risk getting lost -- so long as you follow the marathon course.