Many millions travel by air each day. For most of us, the experience of being in an airport is to be endured rather than appreciated, with little thought for the quality of the architecture. No matter how hard even the world's best architects have tried, it is difficult to make a beautiful airport. And yet such places do exist. Cathedrals of the jet age that offer something of the transcendence of flight even in an era of mass travel and budget fares.  Here are twenty-one of the most beautiful airports in the world.