The VV1 Guide Section of the forum has a thread entitled, "Detailed Spoilers" which explains all the puzzles. I have copied from that thread the solution to the treasure puzzle below. To prevent accidentally revealing a spoiler to other readers, you must highlight the block of text below to make it visible. [begin highlighting HERE-->>]

Puzzle 15 is a buried treasure. Its location can be discovered only by a master builder. Your tribe must also have researched Level 3 in both Construction and Science before they have the technology required to make the discovery. You must actually drop your builder in the right location - dragging him around won't help you find it. Look for the message, "Is something buried here?" to tell you that you're in the right place. Try dropping your builder directly south of the food bin in line with the temple. Once he locates something, you may have to be persistent before he will actually start digging. Keep dropping him there - it could take many, many tries. Once he starts digging, and the scaffolding appears, other builders (if you have any), regardless of skill, will start to help, too!
[<<--end highlighting HERE] I hope that helps!

- Borg