  We present arguments that show why it is difficult to see \emph{rich} extra
dimensions in the Universe. More precisely, we study the conditions under which
significant size and variation of the extra dimensions in a Kaluza-Klein
compactification lead to a black hole in the lower dimensional theory. The idea
is based on the hoop (or trapped surface) conjecture concerning black hole
existence, as well as on the observation that dimensional reduction on
macroscopically large, twisted, or highly dynamical extra dimensions
contributes positively to the energy density in the lower dimensional theory
and can induce gravitational collapse. We analyze these conditions and find
that in an idealized scenario a threshold for the size exists, on the order of
$10^{-19}m$, such that extra dimensions of length above this level must lie
inside black holes, thus shielding them from the view of outside observers. The
threshold is highly dependent on the size of the Universe, leading to the
speculation that in the early stages of evolution truly macroscopic and large
extra dimensions would have been visible.
