  An extension of the single-freeze-out model with thermal and geometric
parameters dependent on the spatial rapidity, $\alpha_\parallel$, is used to
describe the rapidity and transverse-momentum spectra of pions, kaons, protons,
and antiprotons measured at RHIC at $\sqrt{s_{NN}}=200 {\rm GeV}$ by the BRAHMS
collaboration. {\tt THERMINATOR} is used to perform the necessary simulation,
which includes all resonance decays. The result of the fit to the rapidity
spectra in the range of the BRAHMS data is the expected growth of the baryon
and strange chemical potentials with the magnitude of $\alpha_\parallel$, while
the freeze-out temperature is kept fixed. The value of the baryon chemical
potential at $\alpha_\parallel \sim 3$, which is the relevant region for
particles detected at the BRAHMS forward rapidity $y \sim 3$, is about $200
{\rm GeV}$, {\em i.e.} lies in the range of the values obtained for the highest
SPS energy. The chosen geometry of the fireball has a decreasing transverse
size as the magnitude of $\alpha_\parallel$ is increased, which also
corresponds to decreasing transverse flow. This feature is verified by
reproducing the transverse momentum spectra of pions and kaons at various
rapidities. The strange chemical potential obtained from the fit to the
$K^+/K^-$ ratio is such that the local strangeness density in the fireball is
compatible with zero. The resulting rapidity spectra of net protons are
described qualitatively in the model. As a result of the study, the knowledge
of the ``topography'' of the fireball is achieved, making other calculations
possible. As an example, we give predictions for the rapidity spectra of
hyperons.
