  A high-density calorimeter, consisting of magnetized iron planes interleaved
by RPCs, as tracking and timing devices, is a good candidate for a next
generation experiment on atmospheric neutrinos. With 34 kt of mass and in four
years of data taking, this experiment will be sensitive to $\nu_\mu \to \nu_x$
oscillation with $\Delta m^2 > 6 \times 10^{-5}$ and mixing near to maximal and
fully cover the region of oscillation parameters suggested by Super-Kamiokande
results. Moreover, the experimental method will enable to measure the
oscillation parameters from the modulation of the L/E spectrum ($\nu_\mu$
disappearance). For $\Delta m^2 > 3 \times 10^{-3}$ eV$^2$, this experiment can
also establish whether the oscillation occurs into a tau or a sterile neutrino,
by looking for an excess of muon-less events at high energies produced by
upward-going tau neutrinos ($\nu_\tau$ appearance).
