Hallein is the second largest town in the Salzburg province, sitting on the Salzach river about 16 km south of Salzburg. The main reason to visit is the Dürrnberg salt mines above the town — the mines that gave Salzburg ("Salt Fortress") its name and bankrolled its Archbishops for the better part of a thousand years.
The Salzbergwerk Hallein is easily visited on a day trip from Salzburg, reachable by both train and bus. On guided tours, visitors board an electric mine train deep into the caverns, walk through galleries, and change levels by sliding down polished wooden slides — great fun for adults and children alike. An underground museum traces the history of salt mining in the region, and the Keltenmuseum down in town tells the older story of the Iron Age Celts who mined salt here from 600 BC.
The old town of Hallein itself, with its narrow streets along the river, is pleasant for a stroll. The unexpected resident attraction is the Stille Nacht Museum — the house and grave of Franz Xaver Gruber, the organist who composed the music for "Silent Night" in 1818 and is buried here.