This superb structure dates to somewhere around 3000BC.
The mound is 7.3 metres high and 35 metres in diameter. It is surrounded by a ditch and low bank.
The long, low entrance passage leads to the main chamber which is about 4.5 metres square and would have been about 4.5 metres in height; however the roof collapsed after being entered by Norsemen in the 12th century. These raiders left runic graffitti over much of the main chamber stones.
There are three subsidiary chambers in the walls of the main chamber.
At mid winter, the setting sun shines down the passage and shines on the back wall of the tomb.