These photos were also taken by my grandparents while on vacation in 1966. They’re also Kodak slides, and they’ve been scanned but not altered.
The first image is of the Acropolis of Athens, and in this citadel all the other images except the last are found.
The last image is of the Panathenaic Stadium, the location of the Panathenaic Games between the sixth and third centuries BC. The Panathenaic Games were like the Ancient Olympic Games but only Athenians competed. In the late 1800s the stadium was rebuilt, and the first modern Olympic Games took place there in 1896.