Brasov is the obvious base for exploring central Transylvania. Bran Castle is half an hour by car or about an hour by bus from Autogara 2 — it is sold as Dracula's Castle (which it never quite was) but is genuinely impressive on its own terms. The Saxon fortified church at Prejmer, also half an hour away, is a UNESCO-listed survivor of the early 13th-century parish-fortress system; Harman has a similar but smaller example.
Peles Castle at Sinaia, 45 minutes south by train, is one of the most elaborate buildings in Romania — the 1880s summer residence of the Hohenzollern kings, in a self-confident French-Renaissance style. The medieval citadel of Sighisoara is two hours away and easily done as a day trip by train. And in winter, Poiana Brasov is twenty minutes by city bus.
