空城旧梦忆前尘
[kōng chéng jiù mèng yì qián chén]
Refers to nostalgic memories evoked by an empty city ('Old Dreams Remembered in an Empty City'). The feeling is of reminiscing over past emotions or events in solitude. There's a sense of melancholy about revisiting former days, particularly those filled with sweet and bitter remembrances of life.