Info from Babylon Wales
The Mars Bar was a short-lived but interesting alternative music venue with tunes spun by Cardiff’s hippest person of that era Mark Taylor. It opened in 1986 and was, as I recall, a bit of a dive. It was situated above Qui Qui’s on Charles Street. Entrance cost a mere £1 and the beer was also super cheap. Weird videos were shown. You could be forgiven for missing the dance-floor at the rear of the premises obscured as it often was by a liberal application of dry-ice. Unfortunately the people who ran the Mars Bar were forced to change the name when the manufacturers of the chocolate bar threatened to sue them.

The building seems to have been torn down and replaced by flats