Grim's post below about the Merlin cave and it's monument to Merlin- the carving in the rock of the wizards face, brought to mind another monument I'd seen recently, alas not in person but perhaps someday- Sverd i Fjell. It's near Stavenger, Norway and memorializes the battle most symbolic of the unification of Norway, the Battle of Hafrsfjord, where King Harald Hårfagre (Fairhair) united most of Norway under one crown, effectively marking the origins of the modern Norway.
The largest sword represents that of the victorious King Harald, with the two smaller swords representing those of the two defeated petty kings. The swords are about ten meters tall, making them rather impressive in scale. Similarly to Merlin's Cave, it's a beautiful natural location of historic significance, where a memorial has been placed, and in my opinion, in an effective and powerful way, boldly marking the place and presenting some information and raising one's curiosity to learn more about that which is here memorialized, I would think. It also makes it quite clear what it took to give birth to a nation.
While I'm at it- here's another monument in natural stone like Merlin's Cave-
the Löwendenkmal, or Lion of Lucerne.
It's a memorial to Swiss Guards massacred in the French Revolution in 1792 at the Tuileries Palace.
This one I have had the honor of seeing in person. As I recall, having seen it in photographs prior to going there, I was rather surprised at the scale of it. Because of the pool of water in the foreground, photos never really give a true sense of it's scale. The sculpture is about 33 feet long and 18 feet high, not the 1:1 scale I had always assumed in seeing the photos.
Partly because of the sculpture itself, and partly because of the setting, it's quite moving. Mark Twain describes it better than I ever could (from "A Tramp Abroad"):
"The most mournful and moving piece of stone in the world."
"The Lion lies in his lair in the perpendicular face of a low cliff — for he is carved from the living rock of the cliff. His size is colossal, his attitude is noble. His head is bowed, the broken spear is sticking in his shoulder, his protecting paw rests upon the lilies of France. Vines hang down the cliff and wave in the wind, and a clear stream trickles from above and empties into a pond at the base, and in the smooth surface of the pond the lion is mirrored, among the water-lilies.
Around about are green trees and grass. The place is a sheltered, reposeful woodland nook, remote from noise and stir and confusion — and all this is fitting, for lions do die in such places, and not on granite pedestals in public squares fenced with fancy iron railings. The Lion of Lucerne would be impressive anywhere, but nowhere so impressive as where he is."
I think these two monuments are quite powerful, each in their own way. Maybe if I'm lucky, some day I'll win a commission to design a memorial for some event or person of significance. I'd think it a great honor. I would only hope I could do so well as these.