If you just have a part of a day to visit the Argentinean side of the Falls, then you must head yourself towards the Argentinean Iguassu Park, where the Falls are located. If you are in the Brazilian side, you can take a bus to them, crossing the Tancredo Neves Bridge which links Brazil and Argentina. It's a short travel, and you don't need a visa for a one-day visit. Once in Argentine, close to the Falls, you may choose the Upper Circuit or, alternatively, the Lower One. The first is quicker and easier, but the second is more exciting. You will spend about an hour in the Upper circuit, and a little more if you opt for the second.
After that, take a taxi or a bus to Puerto Canoas, and from there to the Devil's Throat (at the heart of the Falls). You will need two hours minimum to do this last part of the visit.
A typical visit to the Argentinean side of the Falls has the elements of the very short visit mentioned above and also an additional tour on the river or in the park.
The Great Adventure - Argentine
It's a trip on boat and jeep (on the Yacaratia path). Tour duration: about an hour.
The Nautical Adventure - Argentine
That's a very short roundtrip on inflatable speed boat: just a 15 minutes trip.
The Nautical Safari - Argentine
A 40 minutes tour in rafts, on the margins of the Iguassu river.
Visit to the city of Puerto Iguazu
A longer visit can include tours on the Parana river or some more distant destinations, like the Jesuit ruins.
Once in Iguassu Falls, you can visit the Paraguay.
The access to Paraguay, which north of the local Brazilian Foz Iguacu city, is usually through a short car trip.
Here are the highlights of a possible visit to the adjacent Paraguay:
The Jesuit ruins
The Jesuit ruins in Paraguay are a Unesco World Heritage and are very similar to the Argentinean Jesuit ruins. The problem is mainly the distances (150 miles), the roads (secondary ones) and the bureaucracy (the necessity of the visa).
The Bertoni Museum
(12 miles/18 Kms from the Iguassu Falls)
The Bertoni Museum is an interesting visiting site for those interested in botanic and zoological issues. Bertoni was a remarkable Suisse scientist (died in 1929), who had an important contribution to the study of the tropical (particularly the Paraguayan) flora and fauna.
The Itaipu Damp
The Itaipu hydroelectric plant can be visited from the Paraguayan side, rather than from Brazil and Foz do Iguacu. If you are in Ciudad del Est, the Itaipu Dam is just 12 miles/20 Kms north.
The Ciudad del Est
This city stands in the other side of the border with Brazil, but you should be very careful about this visit. Ciudad del Est is a great place for shopping and bargains, specially in electric goods, but you should be careful. Ciudad del Est is very different from its Brazilian (Foz do Iguacu) and Argentinean (Puerto Iguacu) neighbours. In it, there isn't the sympathy of the Brazilian people of Foz do Iguacu nor the safety and order of this city, and neither the quietness or the peacefulness of the Argentinean Puerto Iguassu. In Ciudad del Est the contraband prevails (Ciudad del Est is a paradise for smuggling), as do local gangs; isolated tourists may be targeted and find themselves in trouble.