[celticninja]

It's called "the knowledge" and not only do they need to know 20,000 landmarks (things like The Royal Institution of British Architects building, which is not a very touristy landmark at all) they also need to know 20,000 streets and the best route between them. On their test they have to describe a route across London between 2 landmarks and name every road, roundabout, where they should be in the road when there are multiple lanes, one way restrictions and it has to be perfect. It's an incredibly difficult test to pass.