The Karaoke Crown was a place/building/karaoke parlor that was only shown in Pretty Guardian Sailor Moon, that replaced and was the counterpartner of the Game Center Crown
The Karaoke Crown was where the Secret Base of the Sailor Senshi was located. Even before Usagi became a Senshi, she often went there with friends from school to sing and hangout.
Motoki Furuhata was an employee at the parlor and was always seen behind the counter talking to his turtle, Kamekichi, and later, after Nephrite was reborn as a human (Nefukichi), Motoki took pity on him and began to work at the parlor as well.