Climate change is increasing pressure on cities: high temperatures, intensified through the heat island effect, are increasing health concerns, and energy demand while reducing productivity. Common solutions include air conditioning or improving insulation—while ignoring the near infinite amount of cooling potential that lies just beneath our feet. Only metres below the surface, the subsurface temperature can significantly improve thermal comfort during heatwaves. Depending on geology, depth, season, and climate, the underground provides a reliable cooling source. In response to the climate awareness-building movie ‘Don’t Look Up’, this contribution invites the reader to look down instead. Building on past urban underground spaces (UUS) and a literature review on using UUS to adapt to climate change, this chapter advocates for considering UUS in the battle against urban heat. It compiles possible functions of UUS and key considerations to respond to the challenge of maintaining public space. By combining two possible climate change pathways and varying levels of UUS use scenarios, the chapter highlights four scenarios to showcase the impact potential of UUS’ in adapting to climate change and mitigating the urban heat island effect.