The entrance passage
Access to the interior of Maeshowe is by a long, low, narrow entrance passage on the south-western side of the mound.
Made from clay and huge Orkney stones, some of which weigh up to 30 tonnes, the 11-metre (36ft) entrance is made up of two sections - the original inner section and a partially reconstructed outer passage.
During the 1861 excavations, the cairn’s outer passage was found to be in ruins and the exact form of the entrance couldn't be deduced. Because of this, the missing entrance section remains unroofed today and leads the visitor into a reconstructed section of the outer passage.
The innermost surviving section of the outer passage was roofed at a height of 70cm (27.5 inches) so it was assumed that the rest of the passage had been the same.
Blocking stone and "lightbox"
A stone recess marks the point where the outer passage joins the inner passage.
This recess now houses a large stone that was originally found in the passageway. This massive boulder is thought to have been a "blocking stone", which was dragged from its carefully constructed recess to seal off the cairn, when required.
The fact that it would have been easier to seal the cairn from the inside may hint at the chamber's importance as a centre for rituals. Whatever was going on inside Maeshowe seems to have been kept for a select few!
But although the stone was used to prevent access, it did not completely block the passage. The boulder is 12cm (4.7in) lower than the passage roof so, when it was in place, it left a distinct gap.
Given Maeshowe's known winter solstice alignment, it is often suggested this gap is a "lightbox", similar to the one found in Newgrange, in Ireland. It is tempting to think of loose masonry being used to seal this gap and temporarily removed to allow an aperture for the winter sunlight to enter.
However, given the uncertainty surrounding the original entrance, this function cannot be completely verified.
It is just as possible that the gap was simply to allow the circulation of air. If the chamber was used for the burial of the dead, a means of ventilating the interior, prior to any ceremonies within, would not only have been desirable but probably necessary.
The entrance, leads into a large central chamber, from which three smaller side-cells branch off.