Hi, kind travelers. I finally made the decision to visit 4 days in Athens in early October before heading to Santorini for 5 days. I think I can explore a day or two in Athens on foot and with public transportation. But I want to spend the other two days taking guided tours. I'm interested in spirituality and natural beauty. What must I see? Delphi, Corinth, Mycenae, Olympia, Cape Sounio, Aegina Island?