  We propose a pseudo-Nambu-Goldstone inflation where twin waterfall fields
coupled to the inflaton are responsible for the graceful exit from inflation by
a waterfall transition. In this scenario, the $Z_2$ symmetry for the waterfall
fields and the inflaton protects the inflaton potential against dangerous
quantum corrections coming from the waterfall couplings. We show that there is
a wide range of natural model parameters and initial conditions for a
successful inflation and discuss the reheating process by the perturbative
decay of the waterfall field with a $Z_2$ invariant Higgs portal. We also
present a microscopic model for the inflaton couplings to the twin waterfall
fields in the context of a dark QCD with light and heavy quarks.
