Itaipú runs its own visits, and on the Paraguayan side it runs them from the Centro de Recepción de Visitas at Hernandarias, where the Supercarretera leaves Ruta 7. That is the only door. There is no agency to go through and no ticket to buy in advance: you turn up with your passport, register, watch the film and get on the bus, and the bus takes you along the crest of the dam with a guide and stops at the Mirador Central over the spillway. Departures are on the hour from 08:00 to 16:00, every day of the year.
Two things need booking ahead and are worth the trouble. The Modelo Reducido is the 1:100 physical model of the whole scheme — the dam, the head of the reservoir, the tailrace and the Acaray, Yguazú and Monday confluences — built to test the real thing, and it is open Tuesday to Sunday from 14:00 to 16:00 by reservation made by the Thursday before. The Refugio Biológico Tati Yupi is the nearest of Itaipú's reservoir-shore reserves, 30 km up the Supercarretera, with hourly guided circuits, bicycle rides and cachape (ox-cart) trips. Both need the written authorisation collected in person at the CRV first, and on both you drive your own vehicle.
The Iluminación Monumental is Friday and Saturday only, and you accredit at 19:30 in summer or 18:30 in winter. Floodlighting 8 km of concrete is exactly as strange as it sounds, and Hernandarias treats it as a night out.
Around the dam the same operation runs the Museo de la Tierra Guaraní (Tuesday to Sunday, 08:00–17:00), the CIASI wildlife research centre (mornings only, 08:00–11:00), the Hernandarias costanera with the Playa Tacuru Pucu, and the Parque Lineal Manuel Ortiz Guerrero in Ciudad del Este itself.
Be warned about the website before you send anyone to it. ITAIPU's Paraguayan tourism pages are the Brazilian ones in Portuguese; the real Paraguayan visitor information is a nine-page Adobe Express microsite with no phone number on it, and the opening hours live in a PDF on a path left over from the previous website. Ring the CRV or write to [email protected] and confirm before you build a day around any of it.