Buy a ticket to watch a game at Spyros Louis Olympic Stadium. If there's nothing happening while you're in the area, you might like to check if they give a guided tour of the facilities.
This sporting facility is on the to-do lists of many travelers to Marousi. But Spyros Louis Olympic Stadium isn't the area's only drawcard. Parthenon, Acropolis Museum, and Ancient Agora of Athens are some other interesting attractions nearby.