On the Facebook Postcrossing page one day I saw Wendy's offer of this great Mexico City subway map card. By the time I saw it, she had run out but agreed to be in touch when she had more. A short time later I heard from her and we exchanged details. Wendy tells me the Metro system is the main use of transportation in the city and at certain hours of the day it is chaotic. I can imagine it would be, it is huge! I flew into Mexico City once to transfer planes off season on my way to San Jose del Cabo. To this day I can remember that landing - the city went on forever!