Abstract: An underground tornado shelter having a double-hull design is constructed through a rotational molding process from any one of a variety of materials, such as linear medium-density polyethylene. The tornado shelter has a dome-shaped upper half and a hemispherical lower half. Each half includes a flange, an inner wall, and an outer wall. The outer wall may include planar wall portions, indentation portions, and rib portions. The tornado shelter can also have an anchoring system that is integral with the lower half of the shelter and is formed through the same rotational molding process used to shape the rest of the lower half. Pipes can be inserted into the pipe alignment grooves in the anchoring system, and secured in place with plates bolted to the anchoring system across pipe alignment grooves.