This study collaborated with the “Neighbourhoods in Solidarity” (NS) action-research intervention to understand place, social capital, and mental health for older adults in one Swiss town. It used a longitudinal mixed-methods design, combing a pre/post survey with ethnographic observations. It found that place was a recurring theme throughout the NS intervention and how the NS were able to build social capital. Older adults who participated in the NS experienced an increase in structural social capital, but many participants already had high levels of structural social capital before the intervention. Participants did not experience a significant change in cognitive social capital, but this may have been due to a general decline in cognitive social capital in the area. Neither changes in cognitive nor structural social capital predicted depressive symptoms after one year.