A while ago, I got the Holy Mountain quest and found, eventually, that it was a peak on a one-tile island beyond settlement reach. Others have had the same experience. So when in my current game I was again handed this quest I thought "oh, ha ha" and ignored it. Later, I had built religious buildings with no thought for the quest and was very surprised when the "success" message appeared. And what did I find ? (a) The mountain was at the extreme west of the map (a large pangaea): my lands are near the east, and there are two hostile civs (Toku and Genghis) between me and the mountain. (b) I cannot sail there, because my only ports are on the north coast, in a very wide bay with no access east or west due to sea ice. And finally (c) -you've guessed it - it's a peak on a one-tile island, this time surrounded by sea ice and five tiles from any other land. It would appear that the mountain's location is chosen when the quest conditions are met, on the basis that that location has not been visited by any unit belonging to the questing civ. I say this because there are still many peaks on the map which lie outside all cultural borders, on the main landmass,but have all been seen at some time by my Scouts.