上穷碧落下黄泉
shàng​qióng​bì​luò​xià​huáng​quán

to search everywhere

上穷碧落下黄泉 上窮碧落下黃泉 shàng​qióng​bì​luò​xià​huáng​quán
to search everywhere
To search up into the highest heavens and down into the deepest underworld; to leave no stone unturned in an exhaustive search. From a line in the Tang dynasty poem "Song of Everlasting Regret" by Bai Juyi.