An alley cat race is where cyclists navigate from checkpoint to checkpoint around the city. It was originally imported from bike courier culture in america in the mid 90's.
If you've found critical mass a bit slow, this might be your thing, fast racing where everyone is welcome to participate... each checkpoint tells you where to go next, it might be to the top of a multistory carpark, it might be down some alley ways, or on a main road. The main thing about these races are that they are fun, it doesnt really matter who wins or looses...its just about riding together in a group around the city...fast.