Please answer the following question: Omonoia Square -  Omonia Square (Greek: Πλατεία Ομονοίας Plateía Omonoías pronounced [plaˈtia omoˈnias] Concord Square often simply referred to as Omónia [oˈmonia]) is a central square in Athens. It marks the northern corner of the downtown area defined by the city plans of the 19th century and is one of the city's principal traffic hubs. It is served by Omonia train station. Given a choice of categories company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work, the text refers to which one?
A:
Building