Cos'è... una caccia al tesoro??? Troppo forte, non ci posso credere...
The Royal Mail has come in for plenty of flack over recent years but you have to hand it to them on this one. A guy sent a Christmas card with this routing information:
Seriously. No address, postcode or any of that nonsense. Just a rough map and an X marks the rough area type thing. Sure enough, the boys in their red vans and blue overalls tracked Peter O'Leary down and delivered the goods. Outstanding!