The cost of entrance to the Acropolis is about 12 euros and is good for the other sites in the area including the ancient agora, theatre of Dionysos,Kerameikos, Roman Agora, Tower of the Winds and the Temple of Olympian Zeus and is supposedly good for a week.
Walking around Plaka and the street scene at the foot of Acropolis.
A quick countryside visit to the Temple of Poseidon in Sounion, taking 2 hours bus ride, situated on top of a cliff facing the Aegean Sea. Imagine the battles of ancient times that happened on this water.
Acropolis Museum is also a must visit ideally before climbing up the Acropolis grounds. The museum keeps and preserves all the original statues and carvings of the Acropolis site, including the famous Caryatids as shown below. Entrance fee to the museum only costs 5 Euros.