TARDIS staircase

The TARDIS staircase was a vertical pathway between the planetary surface and the TARDIS when hovering in the sky. The entire structure, when viewed from below, was either invisible or cloaked by a perception filter. (TV: The Snowmen)

The lowest few metres were traversed via a retractable ladder extending down from a landing, much like a fire escape ladder. Although invisible from the ground, the ladder could be pulled down by someone who knew precisely where it was and could reach it. (TV: The Snowmen)

The majority of the structure, between the landing and the cloud-top TARDIS, consisted of a spiral staircase. Like the TARDIS itself, the staircase was dimensionally transcendental; a comparatively short climb would traverse considerable altitude. Moreover, the spiral's twist reversed just below its top. For most of the staircase's length, the user climbed up clockwise and down anticlockwise; the top few steps, however, spiralled up anticlockwise and down clockwise. (TV: The Snowmen)