Ultima Thule

 was the supposed location of some treasure. Karl gave the Sixth Doctor the coordinates of its location. (AUDIO: Beyond the Ultimate Adventure)

Undercover Nazi agent Kriemhilde Steiner incorrectly believed that a phoenix egg uncovered near the Crystal Palace in London, 1936, was the "Eagle of ultima Thule". She believed it would bring the Third Reich great power, but when the phoenix hatched, it burned her to death before returning to its home dimension. (COMIC: The Eagle of the Reich)