Here you can find information on how to get to Ancient Olympia by car via Patras.
Athens to Olympia via Patras (331km). This is the road used by most travelers because it is close to the sea and you have some very beautiful imagery throughout the journey. All you have to do is choose the direction of Patras, then follow on to Pyrgos, and then Olympia.
Here you can find information on how to get to Ancient Olympia by car via Langadia.
Athens to Olympia via Tripoli and Langadia (280km). This route will take you through the mountains of Korinthia, through Artemisio tunnel. After the tunnel look for the sign to the right for Ancient Olympia (Αρχαία Ολυμπία) and follow the road through the mountains of Arkadia towards Vytina and Langadia. This trip is more demanding as there are more twists and turns to the road, but it is definitely a very wildlife abundant and beautiful road to travel.
Here you can find information on how to get to Ancient Olympia by car via Allagi.
Athens to Olympia via Tripoli and Megalopolis and Allagi (296km). This route will take you pass the Artemisio tunnel, and Tripoli, continue towards Kalamata. This trip is demanding from to Allagi until Kalo Nero where you turn right towards Krestena. Follow the signs to Krestena and then to Olympia(Please note that some GPS software implementations have different names for Ancient Olympia. It might be spelt Ancient Olympia, Archaia Olymbia, Olibia depending on your GPS maps provider).