Cairn O is situated on Doonaveeragh Mountain over looking the village site on the plateau below. Getting up to O is a bit of a struggle at it is perched on the top of a very overgrown escarpment. There is an ancient overgrown track to the cairn, but I haven't managed to find it yet.
Macalisters 1911 excavation can be seen here in the disturbed ring around the edge of the cairn where they pitched out stones all around in their search for the entrance. The cairn is about 20 meters in diameter and contains a tiny pentagonal chamber, high up in the cairn in the southeast side.
Carn O - A small carn, about 17 feet high and 58 feet in diameter at base, roughly built of stones rather larger than are used elsewhere in the series. Near the top, on the southern side, was a small pentagonal cist, about 3 feet 6 inches high and 4 feet in maximum length, covered with a single slab of stone.
It was entered through an opening 10 inches wide from a manhole, also pentagonal, and covered with two slabs. The floor of the cist was quite irregular and was heaped up with discs of sandstone, bone, and ashes. The height is given on the O. S. map as 890 feet above sea-level.
There is barely room for one person in this tiny chamber which resembles the structure of some of the tiny Carrowmore chambers.
Perhaps it was not intended for people, only burials, as has been suggested of the small chambers at Carrowmore.
The orientation of this chamber is directed away from the rest of the monuments at Carrowkeel, towards Sheemor and Loughcrew 75 km away. It may be aligned towards to the extreme lunar standstill rising or towards another monument, linking Carrowkeel with the sites on the east coast of Ireland.
Cairn P is a smallish round cairn a few hundred meters beyond Cairn O, situated on the highest point of Doonaveeragh Mountain at 283 meters. Standing on the summit of this cairn and looking out across Cairn O and the village, you can see that the whole mountain points to Knocknarea 25 km away.
More than one visitor has been reminded of a gigantic ship upon viewing Doonaveeragh Mountain from the cliffs at the edge of Carrowkeel. Macalister says he spent a few hours digging Cairn P, but gave up concluding the mound was blind or a cenotaph.
Carn P—A beautifully built conical cam, about 12 feet high, and 33 feet in diameter at the base. The Ordnance map gives 138 feet as its height above sea-level. The most careful examination of this carn failed to reveal any cist, chamber, or interment; it is a cenotaph, like Carn A. Four large boulders of rock had been laid on the site chosen for the carn, and the stones were heaped on these.
Today it doesn't look disturbed enough for them to have dug too deeply. Macalister noted that the cairn, which is about 9 meters in diameter, was well constructed on a foundation of four massive boulders.
There is an interesting view from these two cairns. From Cairn O, Cairns G and H are visible, as is the large erratic boulder, but Cairn K cannot be seen. From Cairn P, Cairns G and K are visible, but now H cannot be seen. These two sets of angles offer extra positions to watch midsummer sunsets from.
Cairn P appears to be on a major line which extends from Kesh Cairn to Sheemore in Co. Leitrim, and possibly across the country to Loughcrew.
I have always fancied that Cairn P was used as a lookout by Red Hugh O'Donnell's forces during the Nine Years War (1593 - 1601). His armies used to camp on Doonaveeragh, which overlooks the Red Earls Road, the medieval highway by the mountains. A signal may well have been sent from Cairn P at the commencement of the Battle of the Curlews