The antineutron beam facility built for the OBELIX experiment is described. The set-up for producing antineutrons through the charge-exchange reaction of antiprotons on a liquid-hydrogen target, integrated with the whole detector apparatus, is illustrated. The technique for measuring the intensity of the beam and the energy of antineutrons is explained. Finally, the performances of the facility and its unique features for studying the nucleon-antinucleon dynamics as well as selected topics in meson spectroscopy are reported.