London's Heathrow airport is a place of superlatives. It sees the most international passengers of any airport in the world. It also routinely has the worst delays in Europe and some of the longest lines. (They once snaked out the door and onto the roofs of the parking garages.) Its main airline, British Airways, loses more bags than almost any other carrier—an average of 3,000 a day in 2006. In 2007, fuming passengers hit the carrier with a class-action lawsuit over lost luggage.

While increased security since 9/11 has exacerbated what travelers have come to call Heathrow hell, the main cause is more fundamental: The airport was designed to handle about 45 million passengers a year, and it now serves more than 66 million. Because the system is so overtaxed, even the most minor glitch—a late arrival, a lazy baggage handler, a broken X-ray machine—throws everything off.

But in March, Heathrow will open Terminal 5, an $8.6 billion project spurred by British Airways, which will be the sole carrier in the new space. In development since 1989, the terminal was designed by British architect Richard Rogers, who won the 2007 Pritzker Prize, the Nobel Prize of architecture. It has become the biggest construction project in Europe (two rivers had to be rerouted to make way for it), and B.A. hopes to dazzle passengers with the details. A look at some key features.