Nothing much to add to directions on getting to this site, follow the post by formicaant below but make sure to take the right hand path after parking up as there are two to choose from. If you take the left hand path you will make it there eventually but only after walking through some of the army base.
Both paths seem to be predominantly used though by dog walkers and not solders, on a Sunday at least. Follow the narrow right hand path, which is quite overgrown and enclosed until it opens out at the sign warning you are now entering MOD land. The path does continue on though and you don't have to actually go through any security here, I guess it's just luck whether you run into any patrol or not. The gunfire that could clearly be heard from the base was slightly off putting after just reading the sign but the odd friendly dog walker passing by calmed any nerves.
The long barrow is well enclosed behind barbed wire but looks very well preserved for it. It's not possible to get very close but you can get a good perspective of it without taking the risk of jumping fences onto MOD land. This is a smaller structure by far than the Pimperne long barrow it's closest neighbour.
This long barrow is on M.O.D. land, part of Blandford camp, but public footpaths cross the site so access is allowed. I got there via Tarrant Monkton, drive up a dead end track with a turning circle at its end, park and follow the footpath.
The barrow is well worth the effort, its in great condition, this has been an army camp for two hundred years, so agriculture hasn't harmed it. It has a very wide base, I couldn't get close enough to see any side ditches.
(ST 92940884) Long Barrow (NR). (1) The barrow is situated in the area of military camp and has been fenced around. (2)
(17) LONG BARROW 92950885, on Blandford Race Down. Orientated S.E.-N.W., the mound is parallel-sided, 115 ft. long by 48 ft. wide, and up to 6 ft. high. It may be the one opened in 1840 by J. H. Austen, who found an extended inhumation, probably intrusive, 2 1/2 ft. from the top. (3)
ST 92940884. Long barrow; possibly the one opened by J H Austen and found to contain an extended inhumation, probably of much later date. The barrow mound measures 44 metres long, 18 metres wide and stands up to 1.8 metres high. Scheduling amended. (4)
(17) Long Barrow (92950885), on Blandford Race Down, lies at over 350 ft. above O.D. on a gentle E. slope, just off the crest of a Chalk ridge. Orientated S.E.-N.W., the mound is parallel-sided, 115 ft. long by 48 ft. wide, and up to 6 ft. high. It may be the one opened in 1840 by J. H. Austen, who found an extended inhumation, probably intrusive, 2½ ft. from the top (C.T.D. Pt. 2, No. 27). (O.S., Map of Neolithic Wessex, No. 157.)
(ST 92650920) Settlement (NR). (1)
Small sherds of Iron Age and Romano-British pottery, including a possible small pot base of New Forest ware, were found during investigation. Within the area of the settlement are two probable barrows 'A' (ST 92770918) and 'B' (ST 92540922), both with large central hollows but no surrounding ditches. Dimensions, 7.0m diameter by 0.6m high and 14.8m diameter by 1.3m high respectively. See 1:2500 plan attached. (2) Iron Age and Romano-British settlement 925092 on Blandford Down The site, severely damaged during the present century comprises a nucleated occupation area of about eight acres characterised by low earthworks, now much disturbed, among which a number of sunken platforms are probably the sites of former buildings. The area of occupation lies within a larger area, about 500 yds. in diameter, defined by shallow ditches, low banks and scarps. At least four contemporary tracks in the form of shallow hollow-ways, 25 ft. to 50 ft. across, run into this area. Outside the settlement on the N.E., air photographs show a small subrectangular enclosure (93000947), about 250 ft. by 150 ft., associated with linear ditches and possibly with other enclosures it lies on the N. side of a track which extends E.N.E. from the settlement for at least 1,000 yds., as far as 937097. 'Celtic' fields extend S.W. of the settlement, but nowhere do they join it. (3)
ST 92710924. Iron Age and Romano-British settlement and two Bronze Age bowl barrows on Blandford Race Down. The area occupied by the site has been disturbed by military activity during the 20th century. This disturbance includes a zigzag trench, used for training purposes, probably early in the 20th century. Scheduling amended. (4)