The Temple of Olympian Zeus was the largest temple ever built in Greece. A visit to the site costs €6 as of June 2016, or €30 for a combo ticket including the Acropolis and several other archaeological sites in Athens. The temple can easily be seen for free without entering the grounds, but getting up close gives you an idea of its colossal size and some great views of the Acropolis.
The temple was 96m long by 40m wide. Work began in the 6th century BC and was completed 650 years later in the 2nd century AD under Roman emperor Hadrian. There were originally 104 columns but only 15 remain. They are 17m high. The other columns were dismantled and used for building materials over time.
A few minor structures are located just north of the temple. They include the Themistoclean Wall dating back to around 470 BC, and a set of gates on the wall.
A 5th century basilica, Roman baths, and simple homes can also be found.
To the south of the temple are the Parlissia Sanctuaries. This was a religious center containing a series of temples along the Ilisos River, with the first temples being built in the 5th century BC. The law court for cases of murder was also located there, along with the Temple of Apollo Delphinios.