A coin will form part of a nationwide code-breaking challenge, with the eventual chance for competition entrants to win a gold bar. The £5 denomination coin includes numbers, letters, and symbols that can be used to uncover layers of secrets, riddles and puzzles that form the Great British Treasure Hunt, the Royal Mint said. Level one of the treasure hunt does not form part of the competition. Entrants must successfully complete levels two to five inclusive of the treasure hunt by 11.59pm on March 30. At the culmination of the hunt, those still in the game will have the chance to win the grand prize of a solid gold 250g bar.