Barbarossa in the Untersberg

Emperor Frederick I Barbarossa, who once waged a devastating war in this region in the second half of the 12th century because of he disapproved of who was chosen as the Archbishop of Salzburg1), is now said to be imprisoned with his household within the depths of the Untersberg. Martial music and the ringing of weapons can be heard from the caves of the mountain, especially when war is imminent. Wild knights and squires in glowing armor and flame-wreathed weapons ride on fiery horses through the surrounding regions after midnight, only to return to the mountain as dawn approaches. They vanish into the iron gate which can be seen very rarely by wanderers between the rock formations of the Hallthurm2). Here the bound souls wait while doing good works until that terrible day when unbelief and contemptible lust for power reach their highest level. Then the many people of the world will clash with each other like a whirlwind and meet for a battle on the wide plains of Wals3). There Barbarossa and his followers will turn the tide of battle for the side of Goodness.

Source: Panzer, F. Bayerische Sagen und Bräuche. Beitrag zur deutschen Mythologie. Erster Band, 1848. p. 14.

Notes & Commentary: Weird Locations: The Untersberg, Part 2

The archbishops in question were Eberhard I (took the side of Pope Alexander II and against Barbarossa during the Investiture Controversy) and Conrad of Babenberg (uncle of Barbarossa who refused to recognize Antipope Paschal III and was placed under the Reichsacht - “Imperial Ban” - by the Emperor and thus was branded an outlaw without rights because of this). Conrad's nephew, Adalbert III of Bohemia, initially succeeded him without the Emperor's approval, which caused him to lose the job for six years.
A mountain pass at the northern end of Bischofswiesen, past the ruins of the Plainburg Großgmain.
Presumably the region surrounding the modern Wals-Siezenheim west of Salzburg.