  We experimentally demonstrate the temporary removal of thermal photons from a
microwave mode at 1.45 GHz through its interaction with the spin-polarized
triplet states of photo-excited pentacene molecules doped within a p-terphenyl
crystal at room temperature. The crystal functions electromagnetically as a
narrow-band cryogenic load, removing photons from the otherwise
room-temperature mode via stimulated absorption. The noise temperature of the
microwave mode dropped to $50^{+18}_{-32}$ K (as directly inferred by
noise-power measurements) while the metal walls of the cavity enclosing the
mode remained at room temperature. Simulations based on the same system's
behavior as a maser (which could be characterized more accurately) indicate the
possibility of the mode's temperature sinking to $\sim$10 K (corresponding to
$\sim$140 microwave photons). These observations, when combined with
engineering improvements to deepen the cooling, identify the system as a
narrow-band yet extremely convenient platform -- free of cryogenics, vacuum
chambers and strong magnets -- for realizing low-noise detectors, quantum
memory and quantum-enhanced machines (such as heat engines) based on strong
spin-photon coupling and entanglement at microwave frequencies.
