Geothermal engineer Jay Egg walks through the retrofit of Penn South, a large Manhattan co-op housing complex, from fossil fuel heating to a shared geothermal thermal energy network. Speaking as part of MIT's IAP course RES.ENV-007, Geothermal Energy Networks: Transforming Our Thermal Energy System, Egg traces the project's planning and construction, the borehole fields installed beneath the development, and the practical obstacles of converting an occupied residential community without displacing residents. He covers how the network ties individual buildings into a common loop, the economics that made the conversion viable for a co-op board, and lessons learned that apply to other dense urban retrofits. The talk is a focused case study rather than a general introduction, aimed at viewers who already understand the basic mechanics of ground source heat pumps and want to see how one works at neighborhood scale.