  It is well known that traversable wormholes are valid solutions of the
Einstein field equations, but these structures can only be maintained by
violating the null energy condition. In this paper, we have obtained such
wormhole solutions in an isothermal galactic halo, as well as in a void. We
have shown that the null energy condition is violated, with the help of a
suitable redshift function obtained from flat galactic rotation curves.
