Furnas can keep you busy for a full day if you combine a walk around the lake with a visit to the garden.
The Terra Nostra Garden is the highlight — one of the most beautiful gardens in the Azores, with endemic plants, ponds, streams, and the famous thermal bathing pool. Entry is around 8 euros for adults.
The fumaroles at Lagoa das Furnas are a short walk from town and free to visit. Watch locals lower pots of cozido into the ground in the morning, then return hours later to pull out the fully cooked stew.