ALTENSTEIN, a castle upon a rocky mountain in Saxe-Meiningen, on the south-western slope of the Thüringer Wald, not far from Eisenach. It is the summer residence of the dukes of Meiningen, and is surrounded by a noble park, which contains, among other objects of interest, a remarkable underground cavern, 500 feet long, through which flows a large and rapid stream. Boniface, the apostle of the Germans, lived and preached at Alten-stein in 724; and near the castle is the place from which, in 1521, Luther was seized, to be carried off to the Wartburg. There used to be an old beech called “Luther’s tree,” which association connected with the Reformer, but it was blown down in 1841, and a small monument now stands in its place.