You can go from Cuiabá (Mato Grosso, Brazil) all the way to the sea, over 2800km, by river boat

I've been reading a book on the Paraguay War, Maldita Guerra, and it mentioned how Solano Lopez (then Paraguay's dictator) planned to invade Mato Grosso and possibly take Cuiabá. Trips upstream from Assuncion to Cuiabá at that time would usually take 12+ days on steam ships.

What really surprised me is that this kind of information was supposed to be taught back when I was in school.