One of the best things I ever did was drive cross-country. Seeing the West Coast, Rocky Mountain States, Midwest, South, and East over the span of a few weeks showed me a heck of a lot that I still go back and ponder when I meet someone from a place I passed through. Little tiny things are very different.
But don't underestimate international border culture shock either - especially non-Western countries. America was basically settled by and built on Western European traditions - England, Spain, and France mostly, with some Dutch and later the Irish, Italians, and other Western Europeans. But the ex-Soviet Bloc, Middle East, East Asia are lightyears different from America, and the culture shock is pretty supreme. Basically assumptions about how the world works and should work that I didn't know I had I had to re-check.
The craziest was the Japanese on work. Raised in America, I basically took for granted that doing work is something you don't like that you do for money. Okay, some really lucky people love their jobs, but they're pretty rare. And some people manage to have an "okay job", but all our media, movies, television, and culture ethos are that "work sucks and get it over with so I can get paid and do something else."
Japan? Not the case. People actually take pride in doing work, for working. We look at the Japanese hours and think Japanese people are bat shit crazy, and I mean, maybe they are, but they actually take pride and enjoyment out of working. Comparing an American employee at McDonalds to a Japanese employee at Mosburger or Yoshinoya, or even Japanese McDonalds is a head trip. Cross border culture shock, even. Words don't do it justice, seeing the expression and gesturing and presentation of people working in Japan really is something else, as are similar things in other very different places.