万水千山桑田沧海
[wàn shuĭ qiān shān sāng tián cāng hăi]
These words express the sense of vicissitudes, long distance in geography and long process in history. It means that everything will go through many changes over the long course of history, including the changes from mulberry fields to seas, which often evokes melancholy and reflective moods, indicating one's contemplation on time, experience, or feelings that have been through ups and downs.