From Usk take the B4598 north. Shortly after driving through Llanfair Kilgeddin you come to a left hand turn – park here. Look across the field to your right (crop field) and you will see the long, low mound of the largely ploughed out Barrow.
I was a bit worried about seeing anything with all the snow we have had lately but it wasn’t a problem as most of it had been washed away with the overnight rain.
I think if you visited when the field was in crop you wouldn’t see anything.
Go visit the nearby Coed-Y-Bwnydd Hillfort instead – much better!