It's not easy to get a handle on this one, as it's set in a dense (although small) bit of woodland.
I couldn't see any sign of an entrance to the barrow, although I think that the surrounding ditch is shallower at the eastern end.
Easy to get to from the road/track from Whitsbury village, although you have to walk to the far side of the wood before reaching the break in the surrounding fence.
It's an atmosheric spot (lots of dark twisted trees) and I stayed for quite a while, in spite of lots of pheasant feeding equipment in the area, which made me a bit nervous of being either shot at or accosted by a game keeper.
In an area of several Long barrows you may think you are in Wiltshire, rather than Hampshire. The parish of Whitsbury was part of Wiltshire until 1895, and is still under a Wiltshire parliamentary constituency. This barrow seems to be the most accessible. The fantastic ‘Hampshire Treasures’ resource gives the following info – “Whitsbury Down. 60 m long and 30 m wide. Surrounded by a ditch. In exceptionally good condition. Scheduled Ancient Monument no.448”