Urban green space (UGS) is an essential element in the urban environment, providing multiple ecosystem services as well as beneficial effects on physical and mental health. In a time of societal crisis these effects may be amplified, but ensuring that they are maintained requires effective planning and management - which is a complex challenge given the rapid changes in modern society and the need for continual adaptation. This study aims to identify the drivers that normally attract visitors to UGS, and to assess the effects of social isolation on the usage and perception of UGS during the COVID-19 pandemic. We conducted an online survey during the period in which restrictive measures were imposed in response to the pandemic (March-May 2020), in Croatia, Israel, Italy, Lithuania, Slovenia and Spain. Results showed that urban residents normally have a need for accessible UGS, mainly for physical exercise, relaxing and observing nature. The reduction in UGS visitation during the containment period was related to distinct changes in the motivations of those who did visit, with a relative increase in "necessary activities" such as taking the dog out, and a reduction in activities that could be considered non-essential or high-risk such as meeting people or observing nature. Behavioral changes related to proximity were also observed, with an increase in people walking to small urban gardens nearby (e.g. in Italy) or tree-lined streets (e.g. in Spain, Israel), and people traveling by car to green areas outside the city (e.g. in Lithuania). What the respondents missed the most about UGS during the pandemic was "spending time outdoors" and "meeting other people" - highlighting that during the COVID-19 isolation, UGS was important for providing places of solace and respite, and for allowing exercise and relaxation. Respondents expressed the need for urban greenery even when legally mandated access was limited - and many proposed concrete suggestions for improved urban planning that integrates green spaces of different sizes within the fabric of cities and neighborhoods, so that all residents have access to UGS.