Caer Drewyn is a hillfort near Corwen, in Denbighshire, North Wales. The fort is a site that covers 3 hectares, atop a 290 metre or so high hill, that sits by the town that is about 150 metres above sea level. 

The picture above is the hill that has this hillfort,. There is also a picture of Glyndwr's castle, right at the bottom of this page. 

From the top, you can see down into Corwen, a great almost birds eye view of the town, where the Dee's upper reaches are. From here I am not sure if you can see Glyndwr's castle, I think you can, but did not recognise it from up there, but seeing it is only 2.8 miles east of Corwen, I think it was just I have not been there enough times to recognise the mount. The trees and fields lower along the Dee, look very much like it. 
To the south is Corwen, to the west is Snowdonia, and on a clear day you see the peaks of the mountains. To the North east or east you can even see on a clear day the Clwydian hills, and Moel Famau. On a rainy day you may be lucky to see the trees on the slope to the west above Corwen, and Corwen itself. 

The fort itself, is barely a 2 mile walk from Corwen, but some people park even closer than that in the area below of houses and buildings. So anyhow, it is a nice walk up past the business park, or past the leisure centre, which itself has a nice mural of the fort, which is a rare thing as often hillforts are ignored in terms of the local town. You go up along some nice paths, and curl up round the hill, and can come back down a other route as well, past some houses. The top of the hill, has some fine dry stone walling, which has not been covered in grass, or trees, or earth, and has remained quite square cut in parts. So the walls are pretty impressive in that sense. They form a good shape around the contours of the summit of the hilltop. There is also a area of less than a hectare to the east of the fort on the summit, which some see as a guard place, or something, but it is a interesting extra citadel. 

The fort itself seems to be an Iron Age, structure, that Edward Llwyd said in the 17th Century was a place where locals took cattle in times of war. The fort is now often covered by sheep, like many hillforts, which is good as they do not do much damage to the fort, but make it economical. 

The fort most amazingly was used by Owain Glyndwr as a rallying point for his independence rebellion in the 1400s. Owain Glyndwr was actually from this area indeed his castle or mound, is as I mentioned just east of here. Though actually likely he himself, being a claimant to the title of prince of Wales, had as a local gentry fellow, lived in a fine manor near here, likely a good home, not the mound itself. So he used that mound as a site where he with a band of followers started a rebellion and seems to have had Corwen hillfort as a further rallying point. It is fine to wonder if this was because it was as of a continual memory of the time when it was a Iron Age site. Then again more likely it was just as it continually after then was a site of protection. So on top of that also an earlier Medieval Welsh prince before then, Owain Gwynedd, used Caer Drewyn as the place to rally against English kings, as well in 1165, so it was more to do with that maybe. Although he was maybe copying some Iron Age or Dark Ages inspiration, or stories. 

I do myself say, that there it is a argument it is the 2nd best hillfort in North Wales after Tre;r Ceiri, though maybe Penycloddiau and Moel Hiraddug have a good argument with Holyhead's fort to have that role. Pen Y Gaer aslo. I say this, as it is most in it's pristine condition, and of a good size as well, and such.  So maybe I would put it 3rd or 4th best. Though the Glyndwr history possibly puts it as so tangible so 2nd. 

So I have some pics of the site on the site, or page below, and you can only use them with my permission, I am sure you can make just as good a pics yourself though.