Auto-translated
Sorry for the necro-post, but since the question of finding the Grail remains unanswered, or rather, there's a belief that it involves cheating, I'll say that back in the days when I played on HotS and without rules (i.e., you could place the Grail), I found it with a minimum number of obelisks, sometimes even with just one. Even in the first game of S2TV, where you could still place the Grail, I dug it up with 2 or 3 obelisks. The main idea is to see a piece of land, understand the adjacent terrain type, and if you can see several cells around it, just look – if you have the same type of land nearby, search for that pattern. If you find it, center the screen so that it exactly matches the location in the puzzle, and then draw imaginary lines through the center of the pattern. Most often, the Grail is located somewhere near the center of the puzzle, and you start digging from that point. This is the method used in the second Heroes game.