"There is another wonder in the region which is called Cereticiaun. There is there a mountain, which is given the name Cruc Maur, and there is a grave on the summit of it, and every man whosoever that will come to the grave and stretch himself out next to it, however short they will be, the grave and the man have been found within one length, and, if it will be that the man is short and small, similarly also it is found the length of the grave is like the height of the man, and, if he will be long and tall, even if he might be of length four cubits1 near the height of every man so the tumulus is discovered. And every wanderer who's up to weariness, the man will bow three bows near that, he will not be beyond himself upto his day of death, and he will not be weighted down again by any weariness, even if he will go alone to the boundaries of the cosmos." 2,3
Cruc Mawr ["The Big Hillock/Heap/Tumulus"] is probably the hill Banc-y-Warren near Cardigan4 (Aberteifi), its old name now only indicated by the name of the Farm "Crugmore" on its side (though the actual location is still a little moot5,6). The hill was the site of a major battle (Info) in 11367 , and was mentioned, along with the legend of the grave by Gerald of Wales* in 1187.
You might also like to read more about the Myth of this Wonder or some Visit Details.