Opening line of
欧阳修's (Northern Song)
《蝶恋花·庭院深深深几许》:
庭院深深深几许?杨柳堆烟,帘幕无重数。 (How deep, how deep is the courtyard? Willows piled like mist, curtains beyond counting.) A woman laments her absent lover behind layered courtyards.
李清照 loved the line so much she wrote several poems borrowing the phrase.