Part of our Galaxy is exploding. Recent radio observations show new details of hot gas expanding rapidly from an energetic star-forming region in our Galactic disk out into our Galaxy's halo. The combined power of at least hundreds of supernovae is needed to drive this tremendous expansion. The resulting 1000 light-year mushroom cloud dwarfs any Earth-borne nuclear explosion, but is small compared to the 60,000 light-year diameter of our Milky Way's disk. The mushroom cloud is one of many similar plumes, and provides important clues to the origin and nature of the Milky Way's mysterious hot gas halo.