  We present a numerical code modeling the evolution of the medium formed in
relativistic heavy ion collisions, ECHO-QGP. The code solves relativistic
hydrodynamics in $(3+1)-$D, with dissipative terms included within the
framework of Israel-Stewart theory; it can work both in Minkowskian and in
Bjorken coordinates. Initial conditions are provided through an implementation
of the Glauber model (both Optical and Monte Carlo), while freezeout and
particle generation are based on the Cooper-Frye prescription. The code is
validated against several test problems and shows remarkable stability and
accuracy with the combination of a conservative (shock-capturing) approach and
the high-order methods employed.
  In particular it beautifully agrees with the semi-analytic solution known as
Gubser flow, both in the ideal and in the viscous Israel-Stewart case, up to
very large times and without any ad hoc tuning of the algorithm.
