The main goal of this paper is to present thorough investigations for the metallic nanoshelled structures with rigorous electromagnetic analysis. Two metallic nanoshelled structures are investigated; namely, single nano-shelled cylinder, and nano-shelled photonic crystals. A rigorous Maxwell’s equations solver is used to get insights into the optical properties of the structures. Our numerical simulations show that it is difficult to shift the plasmon resonance to long wavelength (e.g. towards ten micrometers) in such a structure. Flat bands are found in the metallic nanoshelled photonic crystals when the lattice constants are much smaller than the operating wavelength. This would become interesting especially for realizing ultra-compact slow wave structures such as plasmonic devices with low group velocity. Several applications using nano-shelled particles as sensors, as substrates for surface enhanced Raman spectroscopy are also discussed in the paper.