Guidehouse Centre for Renewable Energy Sources and Saving (CRES) Environ Association National Trust EcoFund (NTEF) SEVEn – The Energy Efficiency Center z.ú. Independent Institute for Environmental Issues UfU e.V. Berlin PNEC – Association of Municipalities Polish Network „Energie Cités“ adelphi research gGmbH Energy Cities Romania/ OER Key Take-Aways from Multi-Level Collaboration in the Three4Climate Project