For a sharp mind like yours, it is no doubt rather difficult to find a challenge to stretch the cerebral cortexes. Well, we believe we've found the answer. And it arrives in the form of the ISIS puzzle.You may need to take a seat at this point, as the mind-bending capabilities of this invention could leave you feeling dizzy. Said to be the most difficult puzzle ever, the ISIS carries with it cash prizes for those intelligent enough to crack its code. The ISIS is actually an alloy ball constructed in layers and covered in complex hieroglyphics. But here's the real intrigue - each ISIS requires a different combination to open it. Crack the combination and you'll reveal a special key which opens one of several ISIS golden pyramids hidden in secret locations throughout the UK.

Each pyramid contains a gold coin worth £500 and a number of silver coins worth £20 each.Of course, we'd never leave you to solve such an unfathomable mystery in isolation. There is also an ISIS website to aid you in your quest for the treasure. And once you've beaten this puzzle, don't rest on your laurels. 4 more are in the pipeline.