Millions of passengers use the Mexico City metro daily. It is one of the largest and most used systems in the world, a crowning achievement of the capital's fastpaced growth during the mid-20th Century. A new Gold line, Line 12, is under construction. It will provide a much-needed lateral connection between the lines that snake southward. I ride the metro as often as possible, despite its drawbacks. It is often insanely crowded, and under the hot earth of the Valley of Mexico, the subterrean atmosphere can sometimes be decidely unpleasant. This is a view inside the Hidalgo transfer station.