Try to make it to the Pilgrims' Mass Saturday (not sure if it begins at 10:00 or 11:00). In Jubilee years (like 2004) they 'swing' the Botafumeiro.
The Botafumeiro ritual used to have a practical application: It is an Incense Censer and it would spread spicy incense around to overpower the body odor of hundreds (thousands) of Pilgrims who had been 'on the road' two weeks or more.
I don't care to think about how the Cloister (where many Pilgrims slept) or other parts of the Basilica smelled with the crowds of Pilgrims