Magnons are magnetic waves, resembling ripples on a frozen pond. Their collective dance is described by laws discovered by Bose and Einstein. But at room temperature, a thermal storm ruffles the surface, hiding these ripples. To calm the storm, a film with iron ions is cooled nearly to absolute zero — in such refrigerators typically operate superconducting qubits of quantum computers. In the icy silence, a laser beam, focused to a spot thinner than a hair, illuminates the film. Reflecting, it slightly changes color when a magnon races by — like a siren shifting pitch. This frequency shift, described by Planck, is captured by spectroscopy using an interferometer — a mirror sieve that filters out the desired shades. Simulation revealed an unexpected effect: the beam heated a tiny spot to -272°C, melting a microscopic thawed patch. Contrary to fears, it didn't blur the picture but instead highlighted the waves, like an ice hole revealing a hidden current. If the magnetic track is narrowed to nanoscale sizes, thermodynamic analysis promises quantum measurement of single magnons. Such a bridge between microwaves and light will become a key to quantum information, merging quantum optics and computation into ultrasensitive quantum sensors.