"Man, I've been in their underground part, every 5 years they open for public and open the detectors themselves." This isn't every 5 years, the detectors are a

"Man, I've been in their underground part, every 5 years they open for public and open the detectors themselves." This isn't every 5 years, the detectors are available for the public to visit every winter, and often at other times of the year as well.