I was surprised to learn the LHC collider is not a perfect circle. 27km in circumfrence- 100m underground- it's made made of 8 'arcs' and 8 straight sections with insertion stations in between. It goes under CERN- then some Swiss mountains and into France and then back. That is insane. http://www.lhc-closer.es/php/index.php?i=1&s=3&p=4&e=0
LHC smash protons together in head-on collisions at energy levels higher than ever achieved before. The collider is housed inside the already existing circular tunnel that is almost 27 km in circumference (r = 4243 m) and about 100 metres underground.