You went to Thermopylae? Recommended??
Thermopylae is not like it was then, at least not according to reports from 2500 years ago. It’s wide instead of a narrow passage, which pretty much eliminates any feel for what it was like in the battle. I’d basically say that, no, it’s not worth going far out of your way unless you’re in the neighborhood anyways.
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.