I'm a little grumpy this morning because at this time yesterday, I was riding a bike through Mexico City, where it is 84 degrees. With a souvenir sunburn, I have returned to our gray, gray city. So let me reminisce a little.

Mexico City is the largest city in North America and one of the most polluted in the world. It has insane traffic. The streets feel sort of like New York City, but with fewer laws and a much lower obligation to stop for things like red lights, pedestrians or people selling tamales via bicycle who ride into oncoming traffic.

But every Sunday, the city closes off about 35 miles of its busiest streets to car traffic. Thousands of cyclists, rollerbladers and, yes, white people on Segway tours, flood the empty pavement. This is called Ciclovia and it feels like Portland's Sunday Parkways, in part because Bogota's Ciclovia was the model for our Sunday Parkways. But instead of just sealing off neighborhood streets once a year, it transforms one of the most car-clogged arteries every single week.

My boyfriend and I borrowed crappy mountain bikes from our hotel and hit the streets, stopping to snap photos of the dozens of scouts doing some sort of bike scavenger hunt and the long lines to snag one of the hundreds of yellow bikes Mexico City rents for free for the day. Exhilarating! Awesome! Once we left the closed-off street, though, and headed onto what is supposed to be an on-street bike path through the rest of the city, things turned terrible. The hot asphalt, pollution, wild traffic and bike lane that amounted to just a bike painted on the busy street every block or so combined to make me stop and search for tacos on foot.