Santo Stefano di Sessanio is accessible by car only. The village is about 30 kilometres east of L'Aquila, roughly a 40-minute drive on the SS17 and local mountain roads. From Rome, allow around two hours: take the A24 motorway east towards L'Aquila (the toll road through the Apennines), exit at L'Aquila est, and follow signs east towards Calascio and Santo Stefano.
There is no public transport to the village. L'Aquila has regular bus connections from Rome (around two hours, run by several operators from Tiburtina station) and a train line, but getting from L'Aquila to Santo Stefano without a car is not practical. Car hire is essential if you plan to explore the area properly -- the surrounding villages, Rocca Calascio, and Campo Imperatore are all worth visiting and all require driving on mountain roads.