The great energy source of ultraluminous infrared galaxies (ULIRGs) may be the accreting supermassive black holes of active galactic nuclei (AGNs) or intense concentrations of star formation. While dust obscuration and reprocessing erases the nature of the hidden sources themselves, mid-infrared observations do effectively probe the dust and its distribution in galactic nuclei. Emphasizing spectroscopy obtained with the Spitzer Space Telescope, I will reveal the environments of deeply buried ULIRGs and AGNs, showing that the "torus" of unified AGN schemes is characteristically clumpy and small.