Thousands of cyclists gather in the Argentine capital each month for an event that celebrates the joys of cycling and promotes its positive effect on the city.

Thousands of cyclists from all walks of life regularly gather in Buenos Aires for a communal, organic event that celebrates the joys of cycling and promotes its positive effect on the city.

La Masa Critical (Critical Mass) takes over the streets of the Argentine capital on the first Sunday of each month and every full moon, and the route is completely spontaneous each time.

Critical Mass started in San Francisco, California, in 1992 when a group of cyclists gathered in the city to protest against the traffic. The idea quickly spread to other cities around the world, with cyclists meeting regularly to promote biking as a form of urban transport. 

There is no formal leader, organization or event publicity, and everybody participates for different reasons. Some cycle to make political statements while others join to exercise, see friends or connect with strangers over a mutual passion. Anyone with non-motorized transportation, like rollerblades, skateboards or wheelchairs, can join in, starting and leaving the ride at any point they want.

Participants meet at 4 pm in front of the Obelisk monument on Avenida 9 de Julio. The ride lasts around two hours and ends either back at the starting point or in a local bar.

For visitors to the city who would like to participate, bikes can be rented from La Bicicleta Naranja (50 Argentinean pesos for a half day or 85 Argentinean pesos for a full day, including a helmet and a security lock). La Bicicleta Naranja has offices in Palermo (Nicaragua 4825) and San Telmo (Pasaje Giuffra 308), and bicycles can be picked up and returned to either location. 

Tim Fitzgerald is the Buenos Aires Localite for BBC Travel. He also writes