We see loads of ingenious puzzles here at Firebox, but nothing has ever grabbed us like Isis. Maybe that's because this interactive mind-mangler contains a uniquely coded key that will open one of several golden pyramids hidden throughout the UK - and here's the good bit: the pyramids contain silver and gold coins worth thousands of pounds! Mmm... money.

But before all you puzzlemeisters start booking your flights to St Tropez, there is a slight catch: Isis is said to be the hardest puzzle in the world. In fact its creators reckon it is virtually impossible to crack. The good news, however, is that Isis is one of the most enthralling, mesmerising, infuriating, take-over-your-life puzzles in the history of the universe.

So what's it all about, then? Well, basically, Isis is a gorgeous, handmade alloy orb constructed in layers and covered in cryptic hieroglyphics. All you have to do is open it by cracking the combination. Very Da Vinci Code meets Indiana Jones.

Unlike other puzzles, every Isis is unique, and there are millions of different solutions required to open them. So you'd best get your thinking caps on pronto, because the Isis treasure hunt is a race against time. Indeed the total prize fund is a five-figure sum, plus there will be four more puzzles after this one, each more challenging than the last.

Sadly you can forget about cheating via sledgehammers and power saws; any damage to the Isis will destroy its secret forever. Don't ask us how - we've been too engrossed trying to crack the code to bother cheating. Besides, this precision-engineered puzzle is far too beautiful to vandalise.

Even if you fail to unlock the mystery trapped within this intriguing ball, we guarantee you'll be caught up in the whole immersive experience within seconds of getting your mitts on it. Once you pick Isis up, it's impossible to put down. Especially when you think of all that lovely lolly hiding out there. Ladies and gentleman, your Isis Adventure awaits.