A somewhat literary or historical term for a brothel, often associated with the Edo period or older red-light districts.
In the Edo period, brothels were concentrated in areas called yūkaku (pleasure quarters).
Compound of 妓 (gi, 'courtesan' or 'geisha') and 楼 (rō, 'tall building' or 'tower'), literally meaning a building where courtesans work. The exact historical derivation is uncertain, but the term has been used since the Edo period.