A multi-piece interconnected body for use in at least structural support and/or in creating internal cavities for an improved strength-to-weight ratio in a variety of structures is nestable prior to its assembly and use. When assembled, the device preferably forms a generally spherical and hollow body, with (1) one or more ribs or similar structural support network associated with and/or integrally formed in the body; (2) at least one latch mechanism to help hold the pieces in a desired assembled relationship with each other; and (3) a hinge or other interconnecting element that facilitates nesting and/or stacking of a plurality of the bodies with each other prior to assembly, association of the multiple parts of each body with each other prior to assembly, and ready repositioning of those parts into a desired assembled position.