  We present the results of the one year long observational campaign of the
type II-plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the
Whirlpool Galaxy). This extensive dataset makes SN 2005cs the best observed
low-luminosity, 56Ni-poor type II-plateau event so far and one of the best
core-collapse supernovae ever. The optical and near-infrared spectra show
narrow P-Cygni lines characteristic of this SN family, which are indicative of
a very low expansion velocity (about 1000 km/s) of the ejected material. The
optical light curves cover both the plateau phase and the late-time radioactive
tail, until about 380 days after core-collapse. Numerous unfiltered
observations obtained by amateur astronomers give us the rare opportunity to
monitor the fast rise to maximum light, lasting about 2 days. In addition to
optical observations, we also present near-infrared light curves that (together
with already published UV observations) allow us to construct for the first
time a reliable bolometric light curve for an object of this class. Finally,
comparing the observed data with those derived from a semi-analytic model, we
infer for SN 2005cs a 56Ni mass of about 0.003 solar masses, a total ejected
mass of 8-13 solar masses and an explosion energy of about 3 x 10^50 erg.
