  Multiple observations now suggest that the hydrogen reionization may have
ended well below redshift six. While there has previously been no conclusive
proof of extended neutral islands in the $z < 6$ intergalactic medium, it is
possible that such islands give rise to the giant Ly$\alpha$ absorption troughs
seen in the spectra of high-redshift quasars. Here we present evidence that the
deepest and longest-known Ly$\alpha$ trough at $z < 6$, towards ULAS J0148+0600
(J0148), is associated with damping wing absorption. The evidence comes from a
window of strong Ly$\alpha$ transmission at the edge of the J0148 proximity
zone. We show that the relatively smooth profile of this transmission window is
highly unlikely to arise from resonant absorption alone, but is consistent with
the presence of a damping wing. We further argue that the damping wing is
unlikely to arise from a compact source due to the lack of associated metal
lines, and is more likely to arise from an extended neutral island associated
with the giant Ly$\alpha$ trough. We investigate the physical conditions that
may give rise to the strong transmission window, and speculate that it may
signal an usually deep void, nearby ionizing sources, and/or the recent passage
of an ionization front.
