Above or below?

Each giant detector was built differently. Three were put together deep underground in their caverns. The fourth was assembled in warehouses on the surface and then painstakingly lowered in chunks.

John Osbourne, an engineer working on the LHC says: 'CMS was the only detector largely assembled on the surface and then lowered. One of the reasons we did this was because we knew the underground conditions at the site were so bad.'