I don't know if you've explored the boggy lands on the island where Swamptown is located. If you haven't, I would recommend that you are VERY careful about what you dig up in the NE of the island. I'm not saying don't do it, but you might find it advisable to save your game first.
I would also be rather cautious about where you go in the outside areas on the Isle of Fire - and when investigating some of the whirlpools in the seas around it!
I know this game well, so yell if you need further help. I always play RPGs at least twice, once to get to know the game, and again to play the game to maximum advantage. For example, in the final room of the Tomb of Terror, you will find 4 thrones. These can be extremely useful if you know how, but if your party is good enough to get through Dark Warrior Keep, then it's probably already too advanced for the thrones to be of much help.