  The possibility that the energy density of the Universe is dominated by a
network of low-tension domain walls provides an alternative to the commonly
discussed cosmological constant and scalar-field quintessence models of dark
energy. We quantify the lower bound on the number density of the domain walls
that follows from the observed near-isotropy of the cosmic microwave background
radiation. This bound can be satisfied by a strongly frustrated domain wall
network. No fine-tuning of the parameters of the underlying field theory model
is required. We briefly outline the observational consequences of this model.
