  Exciton-polaritons, hybrid light-matter elementary excitations arising from
the strong coupling regime between excitons in semiconductors and photons in
photonic nanostructures, offer a fruitful playground to explore the physics of
quantum fluids of light as well as to develop all-optical devices. However,
achieving room temperature propagation of polaritons with a large excitonic
fraction, which would be crucial, e.g., for nonlinear light transport in
prospective devices, remains a significant challenge. } Here we report on
experimental studies of exciton-polariton propagation at room temperature in
resonant metasurfaces made from a sub-wavelength lattice of perovskite pillars.
Thanks to the large Rabi splitting, an order of magnitude larger than the
optical phonon energy, the lower polariton band is completely decoupled from
the phonon bath of perovskite crystals. The long lifetime of these cooled
polaritons, in combination with the high group velocity achieved through the
metasurface design, enables long-range propagation regardless of the polariton
excitonic fraction. Remarkably, we observed propagation distances exceeding
hundreds of micrometers at room temperature, even when the polaritons possess a
very high excitonic component, approximately {80}$\%$. Furthermore, the design
of the metasurface introduces an original mechanism for directing
uni-directional propagation through polarization control. This discovery of a
ballistic propagation mode, leveraging high-speed cooled polaritons, heralds a
promising avenue for the development of advanced polaritonic devices.
