Garapata headlands, California
When great headlands meet the sea, great things happen. Among the loveliest of American coastlines, this one is my favorite. I gather Portugal has some nice coastline, and certainly Croatia. Australia too. New Zealand. I'm not sure about Africa. Patagonia! Thailand's karst and the Antarctic Peninsula (though quickly melting).
I would be remiss not to mention that something like half of the entire human enterprise is located on flat lands by the sea, including in river deltas, the flattest of all. Because Antarctica and Greenland store enough water as ice to raise sea level some 300 feet, it behooves us to make damned sure we don't disturb that tenuous status quo, upon which our very civilization is predicated — that sea level is sea level. Unfortunately, we now know that we're in for widespread coastal destruction no matter what we do going forward. Our best students of paleoclimate and the climate system know for certain that we're looking at a minimum of some tens of feet of sea level rise, not the ridiculous, low-ball, misleading figure of "three feet by the end of the century." It's no longer enough to simply stop burning the buried, ancient carbon. Now we have to start actually removing it by the gigaton from the sky, but we don't yet have great ways to do that. If we're going to have much left of civilization a century or two hence, we need to get on this. Now.