I highly recommend the tour of the Itaipu Binacional hydroelectric dam in Foz do Iguaçu, Brazil (well, it's also in Ciudad del Este, Paraguay, but the tour starts from the Brazilian side).

https://turismoitaipu.com.br/en/

Get the "special tour" which takes you inside the dam. An absolutely incredible spot and incredible achievement. They will take you into a room with a turbine shaft that's mechanically transmitting 700 MW of power.