This is a hidden room in the Kabuki market where Johnny plays some guitar and the devs faces flash in a screen before you.
It's really quite a cool easter egg, and the code for the door (605185) was hidden in physical copies of the game, for us digital folk, specially on PC, the only way to get to know about it is through the net.
Thankfully you have me ;)
▶️ 3Speak
