Most travellers come to the south coast for the beaches and the surf. That is completely reasonable. But the coast between Galle and Tangalle has a lot going on inland and offshore that most tourists drive straight past, and the people who find these things tend to say they were the most memorable parts of the trip.
Koggala Lake boat safari. About 15 minutes from Galle toward Ahangama, Koggala is a large inland lake surrounded by mangroves and dotted with small inhabited islands. A guided boat trip takes around one and a half to two hours. You pass through mangrove channels, spot water monitors sunning on the banks, see kingfishers and purple herons, and stop at Cinnamon Island, a working plantation where a local family demonstrates how cinnamon is stripped from the bark and processed. There is a cup of cinnamon tea at the end and, invariably, an attempt to sell you cinnamon products. Buy or politely decline, but go for the lake and the wildlife. Some operators also report small crocodiles near the mangroves, though sightings are not guaranteed. Arrange through your guesthouse or find one of the boat operators near the lake's edge.
Handunugoda Tea Estate. Sri Lanka's famous tea comes from the central highlands, but this estate near Ahangama grows tea at sea level, close to the coast. The most unusual thing it produces is Virgin White Tea, harvested with tongs rather than human hands to preserve the leaves' quality. A visit involves a walk through the plantation, a tour of the factory, and a tasting. It is not a tourist-trap setup. It is a working estate that has been welcoming visitors for years and the guided walk is genuinely interesting if you have never seen how tea goes from bush to cup. About 20 minutes from Weligama or Galle by tuk-tuk.
Cooking classes. A handful of local families and small cooking schools on the south coast offer morning sessions that start at the market, continue with preparing two or three dishes, and end with eating everything you made. Most run in Galle, Weligama, or Ahangama. The cost is usually between 3,500 and 6,000 rupees per person. The quality varies, but the best ones are run by local women cooking the food they actually make at home rather than a tourist-adjusted version of it. Ask your guesthouse who runs the one they would personally recommend.
The stilt fishermen. Still active in Ahangama and Koggala, these are fishermen who balance on wooden poles driven into the shallow water offshore, fishing with rods in the traditional way. They fish in the early morning and late afternoon. You will see them from the road if you are passing at the right time. They are a real part of daily life here, not a performance. Some photographers have taken to hiring fishermen to pose on the poles for money, which has changed the dynamic somewhat in the most popular spots. The fishermen at less-visited stretches are still working authentically.
Matara town. Almost every tourist stops in Mirissa and then drives past Matara to get to Hiriketiya or Tangalle. Matara is a real Sri Lankan town with a Dutch-built star fort from the colonial period, a working fish market at the harbour in the morning, a good local rice-and-curry scene, and Polhena Beach just outside it for turtle snorkelling. It costs nothing to walk through the star fort and the old town, and the fish market is one of the more honest windows into how the south coast actually functions. Spend a morning here rather than heading straight to the next beach.
The south coast rewards curiosity. The best experiences here consistently come from turning inland, asking a local where they would go, and not defaulting to the same five stops that appear on every Instagram itinerary.