On further reflection, I’d modify my comment. Thermopylae was a big letdown when I was there, but probably out of proportion and because of my expectations rather than its merits. Before posting, I should have thought more about whether I was glad I went than about how I felt when I saw it.
I am glad I went while I was already in the area. I’d recommend Thermopylae as a small part of another trip - better than Spanish Rock in Bermuda, or even Mount Rushmore, but nowhere near the value of Gettysburg, where everything is close enough to the original that you can visualize the battle. A historian could spend weeks at Gettysburg and be intellectually engaged every moment; with Thermopylae, an hour or two would be an accomplishment.
Thanks, interesting.