The middle Europe stuff - Brit Isles, France, Germany, Neth, Bel, Swz, Italy, and Greece. Never made it to Former Soviet Union or Eastern Europe, or Scandinavia. I did work with Bechtel and they sent me to a couple of places in the Mideast and I would go to other Mediterranean places from there, to New Guinea (I got to help have a part in building what is now refereed to as 'an environmental disaster'),to India, and all sorts of strange projects in the US. I've been through Mexico and Central America and a thin part of South America. Been to Japan a couple of times too.
I really like Japan for what it is. And Central America is very nice too. But I love the entire Mediterranean deal, the people and cultures around the Sea are agreeable to me. Greece, Italy, Egypt I love the classic tourist classics too so you can't go wrong with the pyramids and the Parthenon. (and I did most of that back in the 80s, when it was still very safe.) Never did Spain, but I want to. I do like the Riviera, I guess everyone does.
But mostly I've traveled the US. The better part of 20 years had huge road trips every year. And I've been on tour (but really that doesn't count, that's work, no fun, it's not like even being somewhere). But on road trips/vacations I've been through most of the US, mostly west of the Mississippi, but not exclusively.I'm a real National Parks junkie and all that stuff is beyond awesome. You can't go wrong at a national park or monument.
But out of anywhere I've ever been, if I had to pick one place to go, it's Tahoe baby. Tahoe and that area has it all. No matter what you want.