Is it weirdly obsessive that I am answering a question that etheral_reality posed, almost two years ago, on the thread??? Probably, but I'm good with that!
e_r posted this picture way back on Page 17
with this text/question "Below: NE corner of Hollywood and Las Palmas.
I wonder where the 'passageway' led to? A mystery for sopas_ej to solve perhaps"
Tonight, as I was continuing my dig through 50 years of LA Herald-Examiner archives, I found that Club 17 was busted for having an illegal gambling parlor in a large hidden room at the back of their building. It had gone undetected for a number of years because, as the owners knew, police monitored all bars for gambling so they had theirs set-up to where gamblers entered through the innocuous little typewriter shop, rather than the club. There was a hidden passageway at the back of the TW shop. The shop owners were, of course, in on the scam and got a small cut of the gambling proceeds. It was suspected that this was one of Mickey Cohen's operations.
and there you have it!