Platform 4 (southbound West Coast intercity main line). I've waited at the foot of the stairs from the footbridge quite a few times over the past twelve years!
The station is cut into the side of Castle Hill. The result is that one can enter the ticket office (the dimly-visible building at the end of the footbridge) at street level then cross the footbridge and descend one storey to platform level, but on the other side of the station, Platforms 2 & 3 are also at street level. Depending on one's chosen entrance, the ticket office is either on the ground floor or, unexpectedly, upstairs.
The even more dimly-visible buildings on the skyline are Lancaster Priory and the castle.