sorry if its too late i have been busy these days...
that shadow below the sign it's the entrance, press enter to get inside.
it's in the capital west side, north of the weapon shop, i don't really remember if the entrance is locked behind a previous quest, i think you can only enter during day time.
Need to go through other events first such as losing the money, working at the pub / tavern in the capital, probably more. The antique store / massage parlor is pretty late game.