hard core: Easton Gym on Beverly 20 some years ago. Jim Morris Gym 25+ years ago
but at 12 years old, I was probably easily impressed 
It’s still there but probably changed. (Easton Gym 8053 Beverly Boulevard Los Angeles). Also Bill Pearls Gym on Manchester is still there.
Mid City Gym in New York City was VERY hardcore. Peals gym on Manchester is still there as well.
Ray Mentzers Muscle Mill was hardcore. So was Barlow’s Gym in Torrance, CA.
Gold's Venice 1981-late 90's when Pete, Tim and Ed still owned it.
World Gym in Lake Forest was cool in the 80’s.
Pete Grymko, Danny Padilla and about 15 of us had keys to a whole in the wall place back in Rochester with a bunch of steel and home-made equipment. It was in the basement of an old German Gymnastics club in a building built in the late early 1900’s. Turner Barbell Club. The pipes leaked, it was freezing cold in the winter and we had to wipe the sweat off the bars in the summer.
This is seldom mentioned but I would have loved to have trained at the Quonset hut in Deland Florida with Arthur Jones when Casey Viator and Sergio were there.
Duncan YMCA in Chicago where Bob Gadja and Sergio trained was supposed to be one of the bst equipped in the country back in the 70’s.
I imagine West-Side Barbell in Ohio is pretty brutal.