On full-moon evenings, Boston Harbor Now’s HarborFit program rolls out mats at Christopher Columbus Waterfront Park, the wisteria-trellised green between the North End and Long Wharf. As the moon climbs over the harbor, an instructor leads a slow, restorative flow with the water — and the occasional ferry — as the backdrop.

This is the mellow end of the HarborFit spectrum: gentle, head-to-toe stretching sequences rather than a sweat session, well suited to beginners, desk-stiff downtown workers, and anyone who wants an excuse to be on the waterfront after dark. Classes are free, though organizers ask you to register ahead since walk-up space is limited. Bring a mat or towel and a water bottle; start times shift through the season along with the moonrise.