This specific 3D model, "skull cave Low-poly 3D model 33", is an asset made available by "Unknown author".
Can be downloaded at "Unknown platform" by following the link.
Usage of this 3d asset is subject to the "Unknown license" agreement.
OBJ (OBJ, filesize: 15 MB), BLEND (Blender, filesize: 15 MB), FBX (Autodesk FBX, filesize: 15 MB)