The Payload Changeout Room (PCR) ...
...is an environmentally controlled clean-room-type enclosure. It has
a set of outer airlock doors with inflatable environmental seals so
that the payload may be transferred from the payload canister into the
PCR without exposure to the external environment.
At least in the shuttle days:
To access a NASA site you must either have a NASA badge (the issuance of which required you to pass a Homeland Security Presidental Directive - 12 or equivalent background check) or be escorted by a properly badged individual. In addition to general site access, you must also be badged for the specific work areas.
To access ...
This is a frame from a video I shot in the Shuttle Mission Simulator back in the 90s. I was sitting in the commander's seat. The shoebox with the red stripes is supposed to be the launch tower, you can see the ground at the bottom.
The simulator window field of view was supposed to be accurate. But although I didn't have a helmet on, I would say yes.