Perth Underground railway station is a railway station within the Perth central business district in Western Australia along the William Street tunnel. It is adjacent to the above-ground Perth railway station and is sometimes considered part of that station. Perth Underground station is served by Yanchep line services heading north and Mandurah line services heading south. It was built as part of the construction for the Mandurah line and was known as William Street station during construction due to its location on William Street. Perth Underground station consists of an island platform and a concourse below ground. There are five entrances to the station: from Murray Street Mall, Raine Square, 140 William Street, underneath the Horseshoe Bridge, and from Perth station.