The Unstan, or Onston, cairn sits on a small grassy promontory jutting out into the salty water of the Stenness loch.

From cairn, the Ring o' Brodgar and Salt Knowe are clearly visible, across the loch to the north-east, and the Deepdale monolith is silhouetted against the western horizon.

From the outside, the structure is not unlike a smaller version of Maeshowe - a grassy mound. Inside, however, we find architecture distinct from Orkney's Maeshowe-type tombs, but sharing some elements.

The Unstan cairn is a classic example of the danger of categorising.

It fits neither in the Maeshowe-style of chambered tomb, or the Orkney-Cromarty design, but is instead a hybrid, incorporating elements of both styles.

Inside, large slabs of Orkney flagstone divide up the main chamber into stalls - a feature typical of many of Orkney's stalled cairns. However, unlike most of these stalled cairns, which tend to be oblong or rectangular, Unstan is circular.

Not only does the circular shape echo the design of Maeshowe, but Unstan also has a side chamber typical of those found within the Maeshowe-type structures.

Because the roof of Unstan is modern, a concrete construction added after the site was taken into State care in 1934, a skylight gives the interior a bright and airy feel. A welcome change for those fed up of scrambling, torch in hand, around the inside of these Neolithic tombs.

The 7.8 metre (25.6 ft) entrance passage is low and narrow. Once inside, the visitor is faced with the side-cell opening, set in the wall directly opposite the entrance. During the 1884 excavations, two crouched skeletons were found within this cell.

The main chamber is 8.4 metres (27.6 ft) long and split into five sections by vertical flagstone slabs - three central stalls and two shelved end-compartments.

Later burials?

When excavated, among the considerable amounts of bone found throughout, were several crouched skeletons.

As mentioned above, two of these were found in the side cell, the rest in the main compartment.

The crouched burials differ greatly from common Neolithic burial practice, in which the remains were brought into the tomb already stripped of flesh. The bones were not necessarily kept together but were mixed and rearranged among those of the tribe's ancestors.

As such, Unstan's crouched skeletons may represent burials made at a later period - probably the last of the inhumations made in the tomb.

Unstan Ware

Along with the human and animal bones, an unusually large quantity of pottery was found scattered across the floor of the tomb. The fragments came from at least 30 Neolithic bowls, the distinct shape and decoration of which was identical to that found at the Knap o' Howar on Papay.

The sheer quantity of these Neolithic bowls found led to this specific style being named after the tomb. It is now known as Unstan Ware.

Unstan Ware was used at settlements such as the Knap o' Howar and was round-bottomed with linear decoration below the rim.

Carvings or 19th century graffiti?

The carved lintel stone in the Unstan Cairn. Click for a larger view.

Like Maeshowe, Unstan appears to have been visited at some time in the past by Norsemen. If they are not later "fakes" - the carved twig runes can still just be seen on the stone that is now set above the entrance to the side cell.

Beside the faint runes is a deeply-cut carving of a bird, pictured above. Although a piece of carved grafitti identifies this as "Pictish marks" the age of the carving is not known.