Escape from the ziggurat with as much treasure as possible.
From the Pickford Bros' site: "The Spectrum and the Amstrad versions were both programmed in BASIC by John and his schoolfriend Paul Ranson, who designed and wrote the games while both still at school in the sixth form." (That is ages 16 to 18 inclusive.)
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This "escape with treasures" game is, although very easy, surprisingly solid for the authors' age. Has only a couple of puzzles worthy of the name, but they are well thought out, and presentation is fine for a BASIC adventure.