Watch the movie Contact. There's an entire scene underneath the dome.

also: http://www.mreclipse.com/Observatory/Arecibo/full/Arecibo03-...

Tom Scott did a video about Arecibo and posted a "behind the scenes" video on his second channel that covers a lot of interesting spaces in and around the telescope.

https://www.youtube.com/watch?v=QZAWqk-wrzc