$10 Military Concrete Bunker Base 2 Low-poly 3D model by AssetSmith. Available on CGTrader with 837 polys and 864 vertices. Check it out on CGHub.
OBJ (OBJ, filesize: 127 KB), MAX (Autodesk 3ds Max, filesize: 2 MB), FBX (Autodesk FBX, filesize: 70.5 MB), PNG (PNG, filesize: 70.3 MB), GLTF (glTF, filesize: 74.4 MB)