It was the very first comics shop I had ever seen. It was the late 1970s and I was allowed to take the Rapid to downtown Cleveland. That was where Cosmic Comics was. I say "allowed" because I was a kid and downtown Cleveland was not the safest place to be at that time. But, hey, my Dad commuted in too. (So did young local weatherman Al Roker, who I would see on the Rapid occasionally, going back and forth to WKYC TV at the time.) Dad worked down Euclid Avenue, teaching at Cleveland State University. Somehow, I argued that I should be allowed a trip up there too. (I then got horribly lost on a loop bus, a story that my Dad and sister love to tell.)
Anyway, Cosmic Comics was owned by Marvel comics writer Tony Isabella and it was the only place for comics in town. Sure, you could maybe buy your Marvel and DC somewhere else, but Cosmic Comics had so many other comics from other publishers. It was the only place you could buy The Comics Journal or The Buyer's Guide. It was the first place I saw Cerebus.
There isn't a lot of serious history or photos about this place, but I know a number of people who grew up to be pros who were regular Cosmic Comics customers. Thanks to one of them, Derf Backderf, here's a piece of video from a 1978 newscast about KISS member Gene Simmons promoting a then-new KISS comic book. He is interviewed by Denny Sanders of radio station WMMS, Cleveland's #1 rock and roll station.