Circle 27 is located by the Kilmackeown Road east of the main monument at Carrowmore.
Circle 27 has a complete ring of huge gneiss boulders, the largest found in the series of circles, originally set standing upright, though now mostly fallen over. There are many fine chunks and bands of quartz in these boulders. There are thirty-seven stones in the circle, which has a diameter of twenty meters. There is an inner circle of smaller stones which is just under fourteen meters in diameter.
Circle 27 has the only cruciform chamber found at Carrowmore. The passage and chamber are formed of thirteen stones, some of split gneiss boulders, and some limestone slabs. There are two limestone slabs which were probably part of a roof. The passage is oriented to the northwest, just to the right of Listoghil, the central monument at Carrowmore, roughly along the axis to the midsummer sunset. The chamber is set in a low stone packing which is bounded by the inner stone circle.
Wood-Martin excavated the chamber in the late 1880's, and found large quantities of cremated and unburnt bone, many fragments of sea shells, pieces of bone and antler pins, pottery fragments, pieces of quartz, and a flat bone ring, thought at the time to be whale bone, but now considered to be walrus ivory. A good quantity of human and animal teeth were found scattered throughout the chamber. A complete account of Wood-Martin's excavation, as printed by Borlase, is given on the next page.
The monument was excavated by Burenhult in the late 1970's. About 8.5 kilograms of cemated and uncremated bones were found, mixed with fragments of sea shells. Fragments of deer antler and bone pins, more pieces of walrus ivory rings, a stone bead, two chalk balls, and thirteen fragments of pottery all came from within the monument.
A small stone cist was found outside the entrance, which had more cremated bone. Several fragments of flint and chert were found outside the chamber, and a flint knife was found just outside the circle.
The monument was carbon dated from charcoal found in the stone packing: c. 3950, 3900 and 3850 cal BC respectively.