"Time Heals" refers to Venusberg.
(ii) An Arthurian country similar to Ys is Lyonesse.
(iii) The primary Arthurian location is Camelot:
"'It was in Britain after the Romans were gone, at the court of a warlord. They called him Riothamus, their High King, but mainly he had some cataphracts. With them he staved off the English invaders. His name was Artorius.'
"Richelieu sat motionless.
"'Oh, I was no knight of his, merely a trader who came by on his rounds,' Lacy stated. 'Nor did I meet any Lancelot or Gawain or Galahad, nor see any glittering camelot. Little of Rome lingered there. In fact, it's only my guess that this was the seed corn of the Arthur legend.'"
-Poul Anderson, The Boat Of A Million Years (London, 1991), XI, pp. 229-230.
Maybe "camelot" should have read "Camelot"?
(iv) Another Arthurian location is Avalon which CS Lewis places on Venus. See Grallon And Arthur. In Anderson's The People of The Wind, two planets in the Lauran System are called "Avalon" and "Camelot." See here.