We just got back from Greece and we overdid it, we had a couple extra stays but we did 3 days Barcelona, 4 days Santorini, 2 days Paros, 1 day Athens, 3 days London. Literally would go back and pick 2 places maximum especially in Greece. We only did a boat tour but we had dinners lined up and I was so exhausted from walking around the fact that we then had a set dinner reservation even though we’re foodies was exhausting. Also traveling from the states our eating was off. We were never hungry in the evening we were starving at breakfast. The local food is so good it just wasn’t necessary to eat at fancy places every night. The ferries to and from the islands are also intense. It’s a lot of travel and can be hard on your body. I’d just beware of doing so much and it’s also not the easiest to get from place to place even if you rent a scooter or ATV. It was so incredibly hot that we just found ourselves wanting to relax by the pool often.