Why is the Large Hadron Collider (CERN) built underground?

Question

...when it would be cheaper to build above ground?

Answer 1

Probably because the underground tunnel was already in existence.  The tunnel was used to house the LEP, an electron-positron collider.

Being underground also provides some degree of protection from potentially dangerous effects.

Answer 2

perhaps it helps minimize minor expansion-contraction and movement that might occur on the surface (a more stable environment underground) combined with the filtering effect of the ground on cosmic particles.  There is a definite reason, because all of these high energy particle colliders are underground.  I am just not positive what the reason is.

I've seen the positron collider at cornell (years ago) and it too is underground. Most remarkable technological systems.

Answer 3

People didn't want the inconvenience of a 27 kilometer long circular particle accelerator snaking is way across picturesque French/Swiss countryside.