  The 21-cm forest is a promising probe of the Epoch of Reionization. The local
state of the intergalactic medium (IGM) is encoded in the spectrum of a
background source (radio-loud quasars or gamma ray burst afterglow) by
absorption at the local 21-cm wavelength, resulting in a continuous and
fluctuating absorption level. Small-scale structures (filaments and minihaloes)
in the IGM are responsible for the strongest absorption features. The
absorption can also be modulated on large scales by inhomogeneous heating and
Wouthuysen-Field coupling.
  We present the results from a simulation that attempts to preserve the
cosmological environment while resolving some of the small-scale structures (a
few kpc resolution in a 50 Mpc/h box). The simulation couples the dynamics and
the ionizing radiative transfer and includes X-ray and Lyman lines radiative
transfer for a detailed physical modelling. As a result we find that soft X-ray
self-shielding, Lyman-alpha self-shielding and shock heating all have an impact
on the predicted values of the 21-cm optical depth of moderately overdense
structures like filaments. An correct treatment of the peculiar velocities is
also critical. Modelling these processes seems necessary for accurate
predictions and can be done only at high enough resolution. As a result, based
on our fiducial model, we estimate that LOFAR should be able to detect a few
(strong) absorptions features in a frequency range of a few tens of MHz for a
20 mJy source located at z=10, while the SKA would extract a large fraction of
the absorption information for the same source.
