The Athens city coastline, extending from the major commercial port of Piraeus to the southernmost suburb of Varkiza for some , is also connected to the City Centre by tram. In the northern suburb of Maroussi, the upgraded main Olympic Complex (known by its Greek acronym OAKA) dominates the skyline. The area has been redeveloped according to a design by the Spanish architect Santiago Calatrava, with steel arches, landscaped gardens, fountains, futuristic glass, and a landmark new blue glass roof which was added to the main stadium. A second Olympic complex, next to the sea at the beach of Palaio Faliro, also features modern stadia, shops and an elevated esplanade. Work is underway to transform the grounds of the old Athens Airport – named Elliniko – in the southern suburbs, into one of the largest landscaped parks in Europe, to be named the Hellenikon Metropolitan Park. Many of the southern suburbs (such as Alimos, Palaio Faliro, Elliniko, Glyfada, Voula, Vouliagmeni and Varkiza) known as the Athens Riviera, host a number of sandy beaches, most of which are operated by the Greek National Tourism Organisation and require an entrance fee. Casinos operate on both Mount Parnitha, some  from downtown Athens (accessible by car or cable car), and the nearby town of Loutraki (accessible by car via the Athens – Corinth National Highway, or the suburban rail service Proastiakos). The large City Centre () of the Greek capital falls directly within the Municipality of Athens or Athens Municipality ()—also City of Athens. Athens Municipality is the largest in population size in Greece. Piraeus also forms a significant city centre on its own, within the Athens Urban Area and it is the second largest in population size within it, with Peristeri, Kallithea and Kypseli following. The Athens Urban Area (), also known as Urban Area of the Capital (), today consists of 40 municipalities, 35 of which make up what is referred to as the Greater Athens municipalities, located within 4 regional units (North Athens, West Athens, Central Athens, South Athens); and a further 5, which make up the Greater Piraeus municipalities, located within the regional unit of Piraeus as mentioned above. The densely built up urban area of the Greek capital sprawls across throughout the Attica Basin and has a total population of 3,074,160 (in 2011).