There is an interesting map in the Venice City Council site, which shows how the Grand Canal, has been formed from what was once a muddy creek draining the lagoon.
It has been Venice's main thoroughfare since the founding of the city and is bordered by succession of fine palaces, almost every one bearing the name of an old Venetian aristocratic family.
It was described by Charles VIII of France's ambassador in 1495 as the "most beautiful street in the world", and it is difficult to think of any rival to that title today.
As there are very few places were you can get down to the Grand Canal on foot, it is best seen from the back of a vaporetto.
Both Routes 1 and 2 run along the whole length of the canal, but Route 1 makes more stops and takes longer.
If possible, try to avoid the crowds by travelling against the flow; that is to say from the Station/Piazzale Roma to San Marco early evening, or vice versa in the morning.