Nothing can prepare you for the sight of these magnificent ruins. They are just simply massive!
If your dates are flexible, I would suggest visiting during low season when the temperature will be cooler and the crowds will be thinner. We were there at the end of March and at high noon, the sun was super hot so I can only imagine how it feels in July. There were a few tourists, of course, but if we waited a bit to let them pass and take their pictures, we had the temples to ourselves after. Incredible.
Once again, if your dates are flexible and if you can travel in the spring, you could visit Sicily during Italian Culture Week. During that week, most culture sites are free. We didn't know that so it was a nice surprise when we arrived. It was free to get in at the Valley of the Temples and free at the Greek Theater in Taormina as well. I think the dates of the culture week change a bit each year but it is always in the spring.









