  We present results of a blind 21cm HI-line imaging survey of a galaxy
overdensity located behind the Milky Way at $\ell,b$ $\approx$ 160 deg, 0.5
deg. The overdensity corresponds to a Zone-of-Avoidance crossing of the
Perseus-Pisces Supercluster filament. Although it is known that this filament
contains an X-ray galaxy cluster (3C129) hosting two strong radio galaxies,
little is known about galaxies associated with this potentially rich cluster
because of the high Galactic dust extinction. We mapped a sky area of $\sim$9.6
sq.deg using the Westerbork Synthesis Radio Telescope in a hexagonal mosaic of
35 pointings observed for 12 hours each, in the radial velocity range $cz =
2400 - 16600$ km/s. The survey has a sensitivity of 0.36 mJy/beam rms at a
velocity resolution of 16.5 km/s. We detected 211 galaxies, 62% of which have a
near-infrared counterpart in the UKIDSS Galactic Plane Survey. We present a
catalogue of the HI properties and an HI atlas containing total intensity maps,
position-velocity diagrams, global HI profiles and UKIDSS counterpart images.
For the resolved galaxies we also present HI velocity fields and radial HI
surface density profiles. A brief analysis of the structures outlined by these
galaxies finds that 87 of them lie at the distance of the Perseus-Pisces
Supercluster ($cz \sim 4000 - 8000$ km/s) and seem to form part of the 3C129
cluster. Further 72 detections trace an overdensity at a velocity of $cz
\approx$ 10000 km/s and seem to coincide with a structure predicted from mass
density reconstructions in the first 2MASS Redshift Survey.
