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Video abstract for the article 'Mapping gigahertz vibrations in a plasmonic--phononic crystal' by Timothy A Kelf, Wataru Hoshii, Paul H Otsuka, Hirotaka Sakuma, Istvan A Veres, Robin M Cole, Sumeet Mahajan, Jeremy J Baumberg, Motonobu Tomoda, Osamu Matsuda and Oliver B Wright (Timothy A Kelf et al 2013 New J. Phys. 15 023013). Read the full article in New Journal of Physics at http://iopscience.iop.org/1367-2630/15/2/023013/article. GENERAL SCIENTIFIC SUMMARY Introduction and background. Metals exhibit plasmonic properties, involving the coupling of electromagnetic fields to electrons, that promise applications in photonic nano-circuits and sensing. The phononic properties of metal structures are also very important in making filters in telecommunications. Here we map for the first time the interaction of the plasmonic and the phononic properties of a periodic solid, that is the 'plasphonic' properties of a plasmonic--phononic crystal. Main results. We fire infrared laser light pulses repetitively to thermoelastically excite high-pitched acoustic vibrations, which are detected by blue light pulses. Our sample consists of a triangular lattice of truncated spherical gold nanovoids each of radius 800 nm, arranged like a close-packed array of tiny golden 'goblets' (see figure). With both light beams tightly focused at one point, we scan the sample laterally over a microscopic area. Images of the reflected blue light intensity oscillations show that there exists an enhanced amplitude in the centre of each nanovoid at around 0.7 GHz (see figure). Numerical simulations of the acoustic field confirm that these oscillations arise from nanovoid vibrational resonances, corresponding to breathing modes. This enhancement suggests that the localized plasmons in each nanovoid are increasing the coupling of both the blue and infrared light to the vibrational modes. Wider implications. We can map vibrations in a plasmonic--phononic crystal, and thereby map the strength of the plasphonic coupling. Engineering both the plasmonic and phononic properties of such crystals to enhance the optomechanical interactions will open up the possibility for novel devices such as acousto-optic modulators.