The West Side Highway
Don't even try running on the walking path when it's gorgeous out. Everyone and their mothers will be out walking at a snail's pace. If you're a serious runner (and not just pretending to be fit because you should take advantage of the nice weather rather than running on a treadmill inside), stick to the bike path. If you're a tourist or looking for a nice stroll, find somewhere else to go or just be aware of actual New Yorkers trying to enjoy their city.
[Photo via @bpcparks]