It shouldn't have been hard to find, really, or to case, it was a reverse-version of the Thieves' Guild guildhall, well, at least the one where Petit was from, might not be anything at all like the one here, reverse or not.
In any case, Petit got to the door first, ushering Belle inside and down the hall to the kitchen, "Welcome to the lair. No idea why we insist on calling it that, really, but it fits."
And it did, really, given as how there was a strong goth-chic influence in all the decor.