Donegal has no rail connection — the County Donegal Railways closed in 1960 and were never replaced. Bus is the main public transport option: Bus Éireann runs services from Dublin (roughly 4 hours) and from Sligo (1 hour 30 minutes). The private bus company Feda O'Donnell runs services between Galway and Donegal via the northwest.
By car, the N15 from Sligo and the N56 along the coast are the main approaches. Donegal is about 265 km north of Dublin — around three hours without traffic. The nearest airports are Donegal Airport (at Carrickfinn on the Gweedore coast, about 60 km north), which has limited connections to Dublin and Glasgow, and Ireland West Airport Knock (roughly 90 km south), with more routes including seasonal international services.
Given the distances between the main sights in the county, a car is strongly recommended for anyone planning to explore beyond the town.