Something went wrong for me: when I first saw the three tombs and the obelisk, I received a message saying that I had already visited them. In the end, I destroyed all the enemies, captured all the mines, but I couldn't complete the game; I couldn't find the artifact. And, of course, the map is quite cramped – there's not much room to move around, and it's difficult to travel by sea.
Hmm... To be honest, I can't say for sure what exactly the problem is. And when you find the obelisk, does a cutscene appear? If so, you need to follow its instructions and fight the final battle for the artifact. The three tombs on the island are for an additional quest; visiting them is not required.
