At the tip of South Boston, in the shadow of Fort Independence, HarborFit brings free tai chi to Castle Island’s grassy waterfront. The class gathers on the lawn near the playground, where instructor Huan Zhang — a sixth-generation practitioner with more than four decades of Chinese martial arts behind him — leads slow, deliberate Yang-style forms as harbor traffic glides past.

Often described as meditation in motion, tai chi rewards patience over power: the coordinated, low-impact movements build balance, ease joint pain, and quiet a busy head, which makes this one of the most genuinely all-ages offerings on Boston Harbor Now’s waterfront fitness slate. Sessions run weekly in season and cost nothing, though advance registration is requested. Bring water and sunscreen — shade is scarce out on the island.