Terceira repays a full day of exploration beyond Angra. The volcanic interior has a large caldera, the Caldeira de Guilherme Moniz, accessible by road and marked walking trails. The Algar do Carvão is a lava tube cave of remarkable proportions — 45 meters deep, with a lake at the bottom and the original lava walls still intact; it's one of the best-accessible volcanic caves in the world and the admission is modest.
On the north coast, the Biscoitos wine region produces distinctive dry white wines from Verdelho grapes grown in the traditional currais — small plots surrounded by low volcanic stone walls that shelter the vines from wind. The wines are available in the local tascas and at the Biscoitos wine museum, which occupies a 19th-century estate winery. The landscape of black lava, pale stone walls, and blue Atlantic is unlike anything else in Portugal.
Terceira also maintains the unique tradition of the tourada à corda — street bullfighting in which the bull is held on a long rope by a team of handlers, allowing it to charge without serious injury to spectators. The events take place in villages across the island from June through September; the full-day festival format, with multiple bulls and dancing in the streets afterward, is something worth planning around if your visit overlaps with the season.