Until the full completion of China’s Three Gorges Dam (scheduled for 2011), the Usina Hidrelética de Itaipu, or Itaipu Dam (Av. Tancedro Neves Km 11, tel. 0800/645-4645, www.itaipu.gov.br, tours 8 a.m., 9 a.m., 10 a.m., 2 p.m., 3 p.m., and 3:30 p.m. Mon.–Sun., R$13) is still the world’s largest hydroelectric power plant. Measuring 8 kilometers (5 miles) in length and 200 meters (657 feet) in height, it currently supplies 25 percent of Brazil’s electricity and 78 percent of Paraguay’s. An amazing feat of engineering, the dam cost a whopping US$18 billion dollars and used enough concrete to build a two-lane highway from Moscow to Lisbon.

Meanwhile, the damming of the Rio Paraná is as controversial as it is impressive. On one hand, Itaipu has been lauded as a safe and nonpolluting energy source that has helped fuel southern Brazil’s incredible economic growth. However, the dam’s social and environmental impact—the loss of Indian settlements, the displacement of 40,000 families, and the destruction and damage of 700 square kilometers (270 square miles) of rainforest—has been severely criticized, despite efforts of Itaipu Binacional (the Brazilian-Paraguayan company that administers the dam) to fund reforestation and relocate animals.

Polemics aside, if you decide to visit Itaipu—located 10 kilometers (6 miles) from Foz—its sheer monumentality is undeniably impressive (although make sure you visit when the spillway is open—otherwise you’re wasting your time).

Ninety minute “panorâmica” visits begin with a 15-minute video showing the dam’s construction followed by an hour-long guided bus tour. Other sights include an ecological museum and a biological nature reserve (guided walking tours to the latter begin at 8 a.m. and 2 p.m.). Friday and Saturday nights at 8:30 p.m., nocturnal tours include a theatrical sound and light show. Hourly buses from the local rodoviária take you to the right to the dam’s visitors center.