Maeshowe Chambered Cairn, where visitors stoop to walk through a narrow entrance passageway before reaching the small, central chamber, has been closed for the past two years.
The finest surviving Neolithic structure in north-west Europe, Maeshowe was built around 5,000 years ago and is regarded as a masterpiece of Neolithic design and construction.
Historic Environment Scotland (HES) lifted the shutters on more than 70 per cent of its estate last year, with the remaining attractions to re-open on a phased basis.
Stephen Duncan, director of marketing and engagement at HES, said: "We are delighted to have even more of our sites such as Maeshowe reopening up and down the country and across our Islands for the summer season, allowing us to again provide visitors with the opportunity to enjoy much loved heritage attractions.
“With over 5,000 years of history in our care, we have adopted a phased approach to reopening a lot of our sites, presenting as diverse a mix of attractions as possible and we are looking forward to welcoming visitors back to enjoy more and more of Scotland’s world-class historic environment after what has been an extremely challenging time for everyone involved in the tourism and heritage sectors.”
Maeshowe is a central part of the Heart of Neolithic Orkney World Heritage Site, which includes the Stones of Steness, Ring of Brodgar and Skara Brae village.
It is believed Maeshowe was built around 2700 BC, the first chambered cairn on Orkney, with the monument surrounded by a ditch and raised bank.
The passage into the central chamber is orientated towards the hills of Hoy and the setting of the sun on the Midwinter Solstice.
Its scale and complexity has led some to speculate that Maeshowe was built for the social elite of Orkney’s prehistoric society.
Maeshowe may have taken 100,000 man hours to construct, it has been claimed.
The monument is also known for its exceptional collection of later Norse runic inscriptions, with more than 33 inscriptions and at least eight sketches or motifs, including the famous ‘Maeshowe Dragon’ or lion. They were reportedly left by a group of Viking warriors who sought shelter in the chamber during a snow storm.