Vol Turin, also known as the Endless Staircase, was a staircase that ran the length of Tronjheim. Vol Turin also had a dwarf sized slide running along its length for dwarves to slide down to the Dwarf city. The staircase leads up to the top of Tronjheim.
Vol Turin's enormous size made it impossible to effectively scale the stairs, so the Dwarves put a slide to the outer rim of it. It is one mile long and takes ten minutes to ride down. Eragon once rode down the slide on Vol Turin, going very fast to the point of ten minutes of blurred vision. When Eragon reached the bottom, he faced Durza and killed the Shade, whilst Arya and Saphira broke the Isidar Mithrim.