  A key role in black hole dynamics is played by the inner horizon; most of the
entropy of a slightly nonextremal charged or rotating black hole is carried
there, and the covariant entropy bound suggests that the rest lies in the
region between the inner and outer horizon. An attempt to match this onto
results of the microstate geometries program suggests that a `Higgs branch' of
underlying long string states of the configuration space realizes the degrees
of freedom on the inner horizon, while the `Coulomb branch' describes the
inter-horizon region and beyond. Support for this proposal comes from an
analysis of the way singularities develop in microstate geometries, and their
close analogy to corresponding structures in fivebrane dynamics. These
singularities signal the opening up of the long string degrees of freedom of
the theory, which are partly visible from the geometry side. A conjectural
picture of the black hole interior is proposed, wherein the long string degrees
of freedom resolve the geometrical singularity on the inner horizon, yet are
sufficiently nonlocal to communicate information to the outer horizon and
beyond.
