Access to the accelerator was surprisingly easy. They offer scheduled tours through parts of the facility during the summer. I didn't need to sign up in advance or even show an ID. (My office, meanwhile, which mostly handles administrative paperwork, has nonsensical security that has x-rayed visitors' coffee cups.)
The large accelerator pictured above is mostly below ground, for shielding purposes as well as prohibitive costs to construct such an enormous building. Here's a bonus exterior photo of a new "small" accelerator: