For many of us, a flavorful, juicy burger oozing with cheese is the very definition of beauty. After all, it's hard to go wrong with a patty wrapped between layers of bread and topped with cheese and crunchy veggies. But, for all the simple, delicious burgers out there, plenty of chefs seem determined to play with flavours and develop new variants of this iconic fast food. So, here is a look at five of the world's best burger joints.