In February 1978, electricity workers digging a trench near the Zocalo struck a huge carved stone disc, and the city found out what lay under its feet. The stone showed the dismembered goddess Coyolxauhqui, and it marked the base of the Templo Mayor, the double temple at the heart of Tenochtitlan. That accident changed Mexico City's idea of itself, and the colonial streets around the cathedral have since been opened up to reveal the Aztec capital below. The historic centre and the canals of Xochimilco, to the south, were inscribed together on the World Heritage list in 1987, because between them they tell how a lake civilisation became a colonial city.
Xochimilco is the survivor of the lake. Its canals and chinampas, narrow artificial islands built up from mud and reeds and planted with maize, flowers and vegetables, were the farms that fed Tenochtitlan, and some of them are still cultivated. Today colourful flat-bottomed boats called trajineras glide along the waterways, bearing families, birthday parties and mariachi bands. The canals are also the last natural home of the axolotl, the strange salamander that keeps its gills for life and can regrow lost limbs, which is now critically endangered.
The ride from the centre to Xochimilco is a slog through the south of one of the largest cities on Earth. The roads are busy and rough, the lights are many, and traffic can slow to a crawl. Use the ring road, the Periferico, where possible, and avoid rush hours, when the traffic is brutal. Many riders weave between lanes, and cars expect it, but newcomers should be careful, especially in the rain, when painted lines and metal covers get slippery. A weekday morning is calmer than a Sunday, when families flood the canals.
Fuel is no problem anywhere in the metropolitan area, and secure parking at the embarcaderos is available for a small fee. The boat ride is slow and sociable, with vendors selling food, drinks and flowers from other boats, and the pace of it is a good counterpoint to the city. In the cool season, the canals are quiet and misty in the early light, and the willows along the banks are lovely. Look out for herons and egrets, and for the narrow strips of chinampa that still push out between the waterways.