This paper describes a nickel-based cellular material, which has the strength of titanium and the density of water. The material's strength arises from size-dependent strengthening of load-bearing nickel struts whose diameter is as small as 17 nm and whose 8 GPa yield strength exceeds that of bulk nickel by up to 4X. The mechanical properties of this material can be controlled by varying the nanometer-scale geometry, with strength varying over the range 90-880 MPa, modulus varying over the range 14-116 GPa, and density varying over the range 880-14500 kg/m3. We refer to this material as a "metallic wood," because it has the high mechanical strength and chemical stability of metal, as well as a density close to that of natural materials such as wood.