Amsterdam Centraal (Dutch pronunciation: [ɑmstər'dɑm sɛn'traːl]; abbreviation: Asd) is the largest railway station of Amsterdam, Netherlands, and a major national railway hub. Used by 162,000 passengers a day, it is the second-busiest railway station in the country after Utrecht Centraal and the most visited national heritage site of the Netherlands. National and international railway services at Amsterdam Centraal are provided by NS, the principal rail operator in the Netherlands. Amsterdam Centraal is the northern terminus of Amsterdam Metro Routes 51, 53, and 54, operated by municipal public transport operator GVB. It is also served by a number of GVB tram and ferry routes as well as local and regional bus routes operated by GVB, Connexxion and EBS. Amsterdam Centraal was designed by Dutch architect Pierre Cuypers and first opened in 1889. It features a Gothic/Renaissance Revival station building and a cast iron platform roof spanning approximately 40 metres. Since 1997, the station building, underground passages, metro station and the surrounding area have been undergoing major reconstruction and renovation works to accommodate the North-South Line metro route, which is due to open in 2018.