The A303 primary route runs close to the southern edge of the site, which by this road is about 2.5 miles (4 km) west of Winterbourne Stoke village.

In the centre of the hillfort lies an earlier and smaller single banked enclosure of 5.2 ha (13 acres) in area, and with an entrance in the western side of the earthwork.

In particular, in the north and east of the site, and between the earlier enclosure and the inner rampart, there are a number of large compounds containing structures clearly visible, many with evidence for possible stone footings.

The local author Ella Noyes (1863–1949) from Sutton Veny[6] wrote in her book Salisbury Plain (1913), the following about the event:[7] Once a year Yarnbury becomes re-animate, on the day of the Horse and Sheep Fair, on the 4 October held in this lonely trysting place by immemorial tradition.

Here.. the flocks..stand close packed in pens; bunches of young ponies are tied up in one corner.. and near by are the sober cart-horses, their plaited manes and tails aprick with ornaments of straw.

But now the pleasure part of the meeting has been abandoned; the folk disperse quietly soon after noon, when business is done, leaving Yarnbury to the silent occupation of its prehistoric ghosts for another year.Yarnbury Castle is located in an area of unimproved grassland on the upper chalk north of the Wylye Valley, and on the edge of Salisbury Plain, which is the largest remaining area of calcareous grassland in north-west Europe.

The local area supports a rich and diverse grassland flora, which led to it being declared a biological Site of Special Scientific Interest in 1951.

[4] The site was previously populated with scattered juniper (Juniperus communis) bushes, but these were removed and the current grazing regime ensures that they do not return.