Saw this, they do massive maintenance every 5 years and do tours in various underground parts.

First of all, I never saw any place better organized, not a smidge of dust, thousands of cables arranged perfectly. And then you get to collider/detector part which is this massive maybe 15m wide long cylinder, opened completely, and it looks like from sci-fi novels.

Just the scale and evident competence of building such a hyper complex unique thing... I live in Switzerland, pretty used to well organized stuff but this was next level.