I wonder how accurate that number is. From what I can find, the source was Castro's head of intelligence. He'd certainly know things, but he is a single source. His list includes things that arent assassination attempts, like assassination schemes (plans that haven't been/won't be put into action) and attempts to assassinate his character. Is a plot to make his beard fall out an assassination attempt?
The scuba suit with poison fungus is one that seems pretty popular, people love to bring it up. But it wasn't an actual attempt, it never made it out of the planning phase.
Wait, the BBC article I just found about his book Executive Action: 634 Ways to Kill Fidel Castro says, "However most of the ideas were never put into practice, former bodyguard Fabian Escalante said." The source of the 634 number isn't even claiming that there were 634 assassination attempts.
It looks pretty similar to this image I found from a British playground equipment site. Odds are it's a real slide in a real room that was furnished after this photo was taken. Outlet looks weird because of the screw holes and the power switches in the middle that UK outlets have.