Didn't realise until today that the Mandarake store in Shibuya was previously a nightclub until the mid 1990s. Can't find any pictures or info at all about this nightclub, but the steampunk-like façade and cave-like interior are more or less untouched since it's nightclub days. Back in the mid 1990s, the original Shibuya Mandarake store was situated in the Dogenzaka area (the Beam Building where Mandarake is now is in Udagawacho), had three floors and was situated up a hill. I think maybe it was right in the middle of Dogenzaka. I've found a scanned article on the store from 1996, but it only shows a picture of the interior and doesn't include the shop's actual address. Not exactly sure when it moved to the nightclub at Beam (circa 1997?), but I do know the store in Dogenzaka opened in 1994.
Edit: there was (maybe still is) a stage inside where staff and customers used to perform karaoke on occasionally. I don't remember there being one, but maybe somehow I missed it every time I've been... apparently this is not the same stage the nightclub originally had. Theirs was a circular stage. Also rather amused to find when people talk about the nightclub on social media, literally no one remembers the name of it.