Sounio is about 70km southeast from Athens.
At pic5 I have pointed out main spots of Attica region, dark blue shows the inland route, light blue the route along the coast.
You can take a suburban bus (KTEL) to Sounio from Plateia Aigyptou (Egyptou square) near Victoria metro station (green line, 2 stops from Monastiraki).
Some buses stops also near Syntagma square (at Fillelinon street near Hard Rock cafe) but you may find it packed. So to be on the safe side and find a free seat take a trolley bus from Syntagma (2,4,5,11,15), all of them stop near Plateia Aigyptou.
There are numerous buses that cover Attica region, check/ask for the one to Sounio and buy your ticket inside the bus. There are 2 different routes:
From Mesogeia (inland route):5.45, 7.45, 9.45, 11,45, 13.45, 15,45
From Attica Coast: 6.30, 8.30, 10.30, 12.30, 14.30, 16.30
The ride may take anywhere between 110-140’ depending on the traffic and the ticket costs about 6 euros
The last bus from Sounio back to Athens departs at 20.00.
You can drive there along the Attica coast passing by upscale coastial suburbs (Glyfada, Vouliagmeni, Voula, Varkiza) and then along other famous beaches (Saronida, Anavyssos, Legrena etc). The route is very scenic.
By tour bus
Sounio is a popular halfday trip from Athens. Most travel agents will offer you a tour there for about 40 euros. If you do this you may want to take the evening tour so to be there for the famous sunset.
I visited Sounio by Athens public bus on 11th October, 2011. The bus station is south-east from metro station Victoria. There was a small board "Sounio-Coastal". Getting in the bus, and pay for the fee in the bus. It costs 6.3 euros for one way. The duration depends on traffic in Athens. In our case, it took two and half hours to get Sounio and two hours to come back.
It's a bit tricky to get to the bus station from where buses depart for Sounio.
Basically, you start from Syntagma Square and take a purple & yellow bus (numbers 5 or 11) towards Plateia Egyptou (Aigyptou Square), past the National Archaeological Museum.
Alternatively you can take the metro to Viktorias. Then make your way east to Oktovriou-Patission and head south. The bus station will be at the intersection with Leof Alexandras.
Driving to this place from Athens can be tricky, with the traffic!
You can easily get to Sounion from Athens KTEL Terminal. Buses run two routes: along the shore (paraliako) and off the shore (mesogiako). The second route is a little longer and more expensive.
The trip should take about 90 minutes as Sounion is 70 km from Athens.
There is a regular municipal bus service to Sounion from Omonia Square, in central Athens (every hour, 4€).
Cape Sounion (or Soúnio) is a promontory located 69 km SSE of Athens, at the southernmost tip of the Attica peninsula.
The site is accessible by road from Athens. This is the scenic highway 91, which closely follows the west coast of Attica (the "Attic riviera"), passing through numerous upscale residential districts and resorts, such as Glyfada, Vouliagmeni, Varkiza. There is a regular municipal bus service to Sounion from Omonia Square, in central Athens (every hour, 1 hour and a half, 4€).
The headland is roughly shaped like an axe-head. A narrow neck of land leads to the higher, gently-sloping site of the temple. On most sides of the axe-head are steep cliffs, up to 60 m high.
You may watch my 2 min 51 sec VIDEO-Clip Athens-Sounio Slide-show out of my VT-Tube or Athens-Sounio Slide-show out of my YouTube with popular Greek music.
It is very easy to get to Sounio by bus from Pl. Aigiptou (between Omonia and Victoria metro stations). It will take you about 1,5-2 hours and about 4 euro to get there. Although it is only 70 km way, but traffic jams in Athens and Glifada are a common thing:(
You can easily get to Sounion from Athens KTEL Terminal. Buses run two routes: along the shore (paraliako) and off the shore (mesogiako). The second route is a little longer and more expensive. The trip should take about an hour as Sounion is 70 km from Athens.
I generally don't recommend travelling through Greece by car. The roads are often crowded and they're used by numerous easy riders.