Rising 253 m at its highest point, Rialto Towers, located at 525 Collins Street, is the tallest reinforced concrete structure in the Southern Hemisphere and a member of the elite World Federation of Great Towers. The observation deck, located on level 55, offers 360-degree views of the city. The building, completed in 1986, houses office space, function rooms, a theatrette, a licensed café bar and an underground carpark. Constructed of reinforced concrete, the two towers (one 63 storeys and the other 43) are encased by glass that mirrors the changing sky. Built by Grollo Australia Pty Ltd, the project architects were Gerard de Preu & Partner and Perrott Lyon Mathieson.