Also is a sex position.
First you need to know what a bicycle is. Its when a guy and a girl does doggy style, but the guy holds the girl's shoulders like handle bars and pedal's his feet like a bicycle.
A town bicycle is when a group of people does the bicycle, but in a line. so the 2nd girl's face is in the 1st girl's crotch. and the 3rd girl's face is in the 2nd girl's crotch, and so on.