I agree with Guardian on the Sites! Having only one lost soul to rescue in a site, and only half of your heroes can get to it, very much illustrates how strong (and annoying) they can be. For artifacts, I think Guardian's suggestions are probably some of the best (and cheapest) to start with. Plus you will also be receiving several Tables of the Law (hopefully) soon! As far as fortresses go, the two I add first are always Wall of Protection or Storehouse (again, I'll be sending you a lot of both), as they are very easy to use and understand.