in niterói the boat terminal and the bus terminal are next to each other - at the niterói bus terminal, bus line 38 can be taken to itaipú.  

this second route is more complicated, but it adds a panoramic portion to the trip, since the boats from praça xv to niterói cross guanabara bay and offer a beautiful view of the bay, of ilha fiscal, of the sugar loaf, and of rio's downtown.

from rio's zona sul, praça xv is easily reachable via taxi in 15 minutes, or via several buses routing along copacabana and ipanema.