Artist Luke Jerram is behind Treasure City where artworks worth at least Â£1,000 each have been hidden around Scunthorpe, North Lincolnshire.
To find and keep the pieces, visitors to the 20-21 Arts Centre in the town must study paintings with codes - some of which are "extremely hard" to crack.
Mathematician and code-setter Dan Fretwell has encrypted the messages.
There was a queue of people eager to see the paintings with the codes as the arts centre opened at 10:00 GMT.
Bristol-based artist Mr Jerram said: "There is no way I could crack the most difficult one, I could certainly crack probably two or three of the paintings.
"Some are really easy to decode, whereas the most complicated painting, it would take maybe a month for someone to perhaps work it out."
Mr Fretwell added: "One of the puzzles may take some months or even years to solve, if indeed it is ever cracked."
The five objects cast into gold for the project are replicas of objects from North Lincolnshire Museum and were made from gold worth Â£1,000. The finished pieces could be worth even more.
The Treasured City exhibition runs until 29 April.
A hunt for five gold art works, which can only be found by cracking clues in five paintings, has started.