  In this paper, we present a series of supersymmetric models exhibiting an
entirely new vacuum structure: towers of metastable vacua with higher and
higher energies. As the number of vacua grows towards infinity, the energy of
the highest vacuum remains fixed while the energy of the true ground state
tends towards zero. We study the instanton-induced tunneling dynamics
associated with such vacuum towers, and find that many distinct decay patterns
along the tower are possible: these include not only regions of vacua
experiencing direct collapses and/or tumbling cascades, but also other regions
of vacua whose stability is protected by ``great walls'' as well as regions of
vacua populating ``forbidden cities'' into which tunnelling cannot occur. We
also discuss possible applications of this setup for the cosmological-constant
problem, for studies of the string landscape, for supersymmetry breaking, and
for Z' phenomenology. Finally, we point out that a limiting case of our setup
yields theories with yet another new vacuum structure: infinite numbers of
degenerate vacua. As a result, the true ground states of such theories are
Bloch waves, with energy eigenvalues approximating a continuum and giving rise
to a vacuum ``band'' structure.
