The historic centre of Siena Low-poly 3D model is available on CGTrader for $24. Original author: SENSIET. Specs: 99348 polys, 75045 verts.
BLEND (Blender, filesize: 21.3 MB), OBJ (OBJ, filesize: 2.28 MB), FBX (Autodesk FBX, filesize: 3.59 MB), TEXTURES (Textures, filesize: 8.08 MB), DAE (Collada, filesize: 10.6 MB), STL (Stereolithography, filesize: 4.74 MB)