Twenty-one stages over three weeks, finishing in Paris, with the route redrawn every year and announced the previous October. Watching is free: the spectator stands at the roadside, waits several hours, is showered with promotional tat by the advertising caravane, and sees the race pass in anything from four seconds on a flat stage to a sustained climb on an Alpine col.
The organiser's widely cited figure is around ten million roadside spectators, from 2018. It is an estimate of a crowd strung along 3,500 kilometres of open road over three weeks, and no counting method can make it precise; we record the year because the number is often quoted without one.
The mountain stages are the ones people travel for, and the Alpe d'Huez or Tourmalet summits are occupied by campervans days in advance.
The route announcement in October is the planning event. Village accommodation along a mountain stage is gone within days of it.
PlanningA moving event, not a place: the route is announced each October and determines everything.