Only 17 kilometers (10.5 miles) across Baía de Guanabara, the well-to-do, suburb-like city of Niterói makes a great day trip. Aside from its long white-sand beaches  and space-age Niemeyer buildings—including the iconic, Star Trek–worthy Museu de Arte Contemporânea  (MAC)—you get to view Rio  in all its dazzling beauty from the other side of the bay.
The most scenic way of getting to Niterói is by taking the ferry that leaves from the Estação das Barcas at Praça XV de Novembro . Boats operated by Conerj (tel. 21/2533-6661)—often jammed with commuters during rush hour—leave at 15–30 minute intervals 7:30 a.m.–midnight and at 60-minute intervals midnight–6 a.m. Ferry rides cost R$2.30.
Quicker and more comfortable, Transtur hydrofoils (tel. 21/2533-4343, R$5) leave at 15-minute intervals, from 6:30 a.m.–9 p.m. Monday–Friday.