Four of five gold artefacts hidden in Scunthorpe as part of a treasure hunt have been found inside a week.
The event is part of an art exhibition at the 20-21 Visual Arts Centre, which began on Saturday 18 February.
To find and keep the pieces, worth at least £1,000 each, people must study five paintings and solve the code within them.
One of the items was found by accident so a reward is being offered to anyone who can solve the clue linked to it.
Artist Luke Jerram said he would donate £500 to a charity of the finder's choice if they could solve the mystery of the "red picture".
The fourth item, the golden train, was found by a family from Grimsby in Scunthorpe's Central Park on Friday night.
Mr Jerram said he had not anticipated so many items would be discovered in the first week.
"I was expecting two or three, something like that. What I did not expect was the response of the public would be so astonishingly positive.
"I did not expect the public would go round looking in every nook and cranny of the town to try and find the artefacts."
The Visual Arts Centre said the public response had been extraordinary.
"It has created a real buzz around the place and brought in thousands of people," said the centre's visual arts officer Michelle Lally.
The final item to be found is the gold copy of a Jurassic ammonite, an ancient marine mollusc fossil.
The five objects are replicas of pieces at North Lincolnshire Museum and were made from gold worth £1,000, but could be worth much more.