Hadron Collider: Inside one of Cern's particle detectors
Measuring 15m (49ft) across, the Compact Muon Solenoid (CMS) is one of the particle detectors at the Large Hadron Collider (LHC) at Cern.
The CMS was switched off for maintenance when BBC Click visited allowing Spencer Kelly to be given a rare chance to glimpse inside it.
In 2012, the LHC detected the sub-atomic Higgs boson particle. The Higgs is a cornerstone of the Standard Model theory, which explains how particles interact.
Scientists working at the LHC announced the discovery of a new particle called the pentaquark in 2015. It was first predicted to exist in the 1960s, but was not proven until its detection at the LHC.