$22 Spiral Staircase v4 Architectural Stairs 270 3D model by modernarchstudio. Available on CGTrader. Check it out on CGHub.
STL (Stereolithography, filesize: 67.8 MB), OBJ (OBJ, filesize: 177 MB), 3DS (3D Studio, filesize: 34.2 MB), DWG (AutoCAD, filesize: 35.1 MB), 3DM (Rhinoceros 3D, filesize: 10.6 MB)