The pride of Paraguay is one of the biggest hydroelectric projects in the world and actually produces 18 times more electricity than Paraguay needs (the remainder is sold to Brazil and Argentina). Although it has proved an economic boon to the area, it has an ambiguous past; its $25-billion price tag plunged all three border countries into debt and had a devastating effect on the surrounding environment. The submerged Sete Quedas falls were actually larger and more impressive than Iguazú. It has also proved a magnet for mosquitoes, boosting the risk of malaria in the area. Nevertheless, it is an engineering masterpiece, impressive in its size, volume, and ugliness. There are two types of tours. One is free via bus, where you cross the dam but see very little of the facility, and another costs $15, but is more technical and you get to disembark. This is recommended as you get to see the 1km-long (about a half mile) machine room. Tours also include a rather technical 30-minute film. On Fridays and Saturdays at 7pm, there is a nighttime illumination and fireworks display. The dam is 20km (12 miles) north of the city, near the town of Hernadarias. Don't forget: Bring your passport!