  The Pulsar Wind Nebula (PWN) 3C 58 is energized by one of the highest
spin-down power pulsars known (5% of Crab pulsar) and it has been compared to
the Crab Nebula due to their morphological similarities. This object was
detected by Fermi-LAT with a spectrum extending beyond 100 GeV. We analyzed 81
hours of 3C 58 data taken with the MAGIC telescopes and we detected VHE
gamma-ray emission for the first time at TeV energies with a significance of
5.7 sigma and an integral flux of 0.65% C.U. above 1 TeV. The differential
energy spectrum between 400 GeV and 10 TeV is well described by a power-law
function $d\Phi/dE=f_{o}(E/1TeV)^{-\Gamma}$ with
$f_{o}=(2.0\pm0.4stat\pm0.6sys) 10^{-13}cm^{-2}s^{-1}TeV^{-1}$ and
$\Gamma=2.4\pm0.2sta\pm0.2sys$. This leads 3C 58 to be the least luminous PWN
ever detected at VHE and the one with the lowest flux at VHE to date. According
to time-dependent models in which electrons up-scatter photon fields, the best
representation favors a distance to the PWN of 2 kpc and FIR comparable to CMB
photon fields. If we consider an unexpectedly high FIR density, the data can
also be reproduced by models assuming a 3.2 kpc distance. A low magnetic field,
far from equipartition, is required to explain the VHE data. Hadronic
contribution from the hosting supernova remnant (SNR) requires unrealistic
energy budget given the density of the medium, disfavoring cosmic ray
acceleration in the SNR as origin of the VHE gamma-ray emission.
