Challenge: The session addresses the question of how to decarbonise buildings in urban space. Buildings are responsible for 28% of global CO2 emissions, largely due to their heating and cooling needs. In cities and metropolitan areas there is a lack of space and technology options to generate and provide green heating and cooling. Solution: Using what is already there: energy from wastewater. Every day we flush vast amounts of energy away through the sewerage system and lose it instead of using it. Energy from wastewater can be easily recovered. This is energy-efficient, cost-effective and takes place invisibly underground. This energy can be used to heat and cool buildings. Applicability: Wherever there are people, there is wastewater. Wherever there are people, there is a need for heating and/or cooling. So supply and demand match perfectly. Energy recovery from wastewater can be realised almost anywhere in the world. This approach can contribute significantly to the decarbonisation of the building sector. The participants will understand that many technologies are already there, but the way to implementation is unclear. People who have not done so before will have to work and talk with each other. Looking beyond the horizon opens up potential that is closer than you think.