It's a temporary wall to protect the road from construction on the other side. Some sort of electrical infrastructure stuff where they gotta dig a big hole.
It was actually taken down today, after being up for over a year. I guess they're finishing up.
That's all urban legend. The real reason no one stays in for more than half an hour is that the lab is busy and they need their anechoic chamber. Not for some rando to just hang out inside of.
$20 a year is an unreasonable subscription model?