Complex sentence: The Kamatchka was just actually a boiler house that also served as a performance venue for rock artists, and was popular among the fans of Viktor Tsoi, who once worked there as a firefighter and also regularly performed there.
Split into simpler sentences: The Kamatchka was just actually a boiler house that also served as a performance venue for rock artists. The venue was well-known to the fans of Viktor Tsoi, who once worked there as a firefighter and also regularly performed there.