As for cracking Atlas Park or any other map for that matter,
Just grab or make a demorecord of a map, and press F2 while running the demo to mouselook and move around on your own. The demo will continue to loop doing whatever it does, but your character will now be under your control.
This works in I23+ clients, so you should be able to do it if your client was from when the game closed.
Also, you can use Cameraman to speed up the movement, since it is a crawl normally in F2 mode.
There's other posts around this site if you search, for more details and nuances.