The region of Attica surrounding the city of Athens is mountainous, alternating with valleys formed between the peaks. Athens is surrounded by several mountains: Parnitha, Egaleo, Penteli, Ymittos and Keratovouni and Paneionin the Lavrion area. Between them lie four valleys interrupted my smaller hills (Tourkovounia, Lecabettous, Strefis, Kolonos Agoraios, Areopagus, Acropolis, the Hill of the Nymphs, Pnyx, Filopapappou, Ardittos), while the southwest part of the city is open to the sea.
The two main rivers of Athens are the Kifissos and the Ilissos. Both are streams during the dry seasons, but in periods of intense rainfall they turn into torrents quite often creating floods. The Kifissos River springs from Parnitha Mountain and flows into the gulf of Faliro after passing through the city. On the other hand, the Ilissos River springs from the foothills of Ymittos Mountain and even today it still flows into the same gulf. However, before the mid 20th century, when its riverbed was diverted in order to channel its waters directly into the gulf of Faliro, it had a different course, running west of Ymittos to join the Kifissos River. Nowadays, both these rivers have been covered and they flow underground.
The course of the Eridanos River, the third and smaller river that sprung from the southern slope of Lecabettous hill and joined the Ilissos River, can only be partly seen nowadays in the heart of the city of Athens.