  The topological structure of the QCD vacuum can be probed by monitoring the
spatial localization of the low-lying Dirac eigenmodes. This approach can be
pursued on the lattice, and unlike the traditional one requires no smoothing of
the gauge field. I review recent lattice studies, attempting to extract a
consistent description. What emerges is a picture of the vacuum as a
``topological sandwich'' of alternating, infinitely thin 3d layers of opposite
topological charge, as originally seen in direct measurements of the
topological charge density.
