Handunugoda Tea Estate gives Unawatuna visitors a look at Sri Lanka's tea culture without travelling all the way into the central highlands. The estate grows low-country tea and is best known for its white tea, with tours that move from garden to factory to tasting room.
It is a short inland excursion rather than a beach activity, and that contrast is exactly the point. Combine it with Galle or other countryside stops, and go with enough time to linger over the tasting rather than treating it as a quick souvenir run.