$22 Spiral Staircase v5 Architectural Stairs 180 3D model by modernarchstudio. Available on CGTrader. Check it out on CGHub.
STL (Stereolithography, filesize: 71.4 MB), OBJ (OBJ, filesize: 188 MB), 3DM (Rhinoceros 3D, filesize: 10 MB), 3DS (3D Studio, filesize: 36 MB), DWG (AutoCAD, filesize: 36.9 MB)