GALAXIES are surrounded by large haloes of hot gas(1) which must be replenished as the gas cools, This has led to the concept(2) of galactic ’chimneys’-cavities in the interstellar medium, created by multiple supernova explosions, that can act as conduits for the efficient transport of hot gas from a galaxy’s disk to its halo. Here we present a high-resolution map of atomic hydrogen in the Perseus arm of our Galaxy, which shows clear evidence for the existence of such a chimney, This chimney appears to have been formed by the energetic winds from a cluster of young massive stars, and may currently have reached the stage of blowing out into the halo.