The prototype in Piedicastello will demonstrate the feasibility of exchanging heat with the surrounding ground through the geostructure, namely the tunnel, for serving a specific building and/or infrastructure. However, metro tunnels and other types of underground structures very often exist in or close to urban centres. Therefore, the technology is optimal for a local harvesting and for widespread distribution of thermal energy at both single space and district scales and could be integrated in low-temperature district heating and cooling networks. The technology potential may be even enhanced by coupling it with other renewable energy-based systems, such as for instance solar collectors. This coupling can lead to interesting applications such as Underground Thermal Energy Storages (UTES). The integration of solar panels for hot water production with the geothermal loops can provide thermal storage abilities to the system and can be used as a thermal source for low-enthalpy energy storage in the ground. This innovative integrated system would allow to buffer differences between thermal supply/demand at a local level, which is particularly attractive due to the inherent asymmetry nature of intermittent renewable energy sources. Tunnels could thus benefit from a smart and sustainable approach and be retrofitted for transforming them into energy generators having positive impacts in terms of social and economic activities.