The Orchid Cage

On a distant planet, not too different from Earth, there stands a mechanized city with no visible inhabitants. Obviously of a highly developed civilization, the question is who built it, where are they, and what can humans learn from them? Two teams of explorers enter into a competition to find the answers. There are no holds barred - almost anything goes to win the contest. But the city is capable of meeting trickery with trickery, violence with violence - and murder with justice. (from the back cover of the DAW Books first English language edition)