Wizards who cannot Apparate (dematerialise and reappear at will), who wish to travel by daylight (meaning that broomsticks, Thestrals, flying cars and dragons are inappropriate), or whose destination has no fireplace (rendering Floo powder useless) will have to resort to the use of a Portkey.
Almost any inanimate object can be turned into a Portkey. Once bewitched, the object will transport anyone who grasps it to a pre-arranged destination. A Portkey may also be enchanted to transport the grasper (or graspers) only at a given time. In this way, the arrivals and departures of great numbers of witches and wizards can be staggered, enabling such events such as the Quidditch World Cup to take place with few security breaches.
When secrecy is paramount, and mass movement is planned, the chosen Portkey will be a nondescript object secreted in an out-of-the-way place, so that it will be taken for a piece of unimportant debris by Muggle passers-by. Accidents have occurred, however; two Muggle dog-walkers found themselves accidentally transported to a Celestina Warbeck concert in 2003, because their dogs had run off with an old trainer on Clapham Common (leaving an anguished crowd of witches and wizards to look frantically for their Portkey on a stretch of empty grass, hopefully seizing old crisp packets and cigarette ends). One of the Muggle dog-walkers was even invited on stage by Celestina to perform a duet of ‘A Cauldron Full of Hot, Strong Love’. While the Memory Charm placed upon him by a harried Ministry official seemed to take at the time, he has since written a popular Muggle song that bears an uncanny resemblance to Celestina’s worldwide hit (Ms Warbeck is not amused).
The sensation of travelling by Portkey is universally agreed to be uncomfortable, if not downright unpleasant, and can lead to nausea, giddiness and worse. Healers recommend that the elderly, pregnant and infirm avoid using Portkeys. The suggestion of arranging Portkeys for the transportation of annoying relatives has saved many a wizarding family Christmas.
The name ‘Portkey’ comes from the French ‘porter’ – to carry – and the word ‘key’, in the sense of secret or trick. I don’t like to boast, but I own a real Portkey – the key to the US city of LaPorte – which was given to me by Emerson Spartz, the founder of the fansite Mugglenet.com.