The Centre for Underground Physics in Pyhäsalmi (CUPP) project is aiming to establish an underground laboratory in the Pyhäsalmi zinc mine, offering a potential location for small-to-medium-scale scientific experiments, which require, e.g., a low level of background radiation. The pilot experiment of CUPP was Muons UnderGround (MUG), consisting of muon detectors placed at different depths. Since 1.1.2001 MUG experiment has been a part of Sodankylä Geophysical Observatory / University of Oulu. At the moment MUG extends the field of cosmic-ray and heliospheric research of the University of Oulu to underground studies in addition to the longterm neutron monitor observations of cosmic rays on ground level in Oulu. As the first active experiment of the CUPP project, the MUG experiment is also used to evaluate and prove the suitability of the facilities of the Pyhäsalmi mine for underground scientific work.

The MUG experiment includes five detector units consisting of three pairs of vertically overlapping plastic scintillators, each equipped with standard NIM electronics and a personal computer for data storage. A data acquisition unit designed and manufactured by Detection Technology Inc is used for data recording and pulse height AD-conversion. A substantial part of the equipment is borrowed from the Space Research Laboratory of the University of Turku. One of the MUG units is on the ground level, two in a cavern 210 m underground, and one in a container 90 m underground. One unit is placed to Oulu Cosmic Ray station.