Staircase tower

Staircase tower with no external door on the church of Saint-Pierre-ès-Liens in Rampoux (Lot), France

A staircase tower or stair tower (German: Treppenturm, also Stiegenturm or Wendelstein) is a tower-like wing of a building with a circular or polygonal plan that contains a stairwell, usually a helical staircase.