All Challenge Tombs can also be found within the regular walkthrough gefunden. Since it's not always clear where they can be found and I don't want to to have to search for them in all possible levels, I now provide this list.

• Glacial Cavern
  • Ice Ship (originally within the level "Best Laid Plans")
• Soviet Installation
  • Ancient Cistern (originally within the level "Unexpected Discovery")
  • Voice of God (originally within the level "Alone Again")
  The rest has not been translated yet. If you are in desperate need, you may want to try the German version of the page and use google translate.