The Iguazu Falls belong to the new seven natural wonders of the world and can be visited from the Brazilian and Argentine sides. The Brazilian side has significantly fewer hiking trails, but the more beautiful Panaroma view. You should see both sides.
From the bus terminal in Puerto Iguazu there are buses to Brazil. You can either drive into the city (Foz de Iguazu) or directly to the waterfalls. Those that drive directly are marked with Cataratas Brasil. The trip was cheap and not more expensive than the buses to the falls in Argentina. If you are traveling to Brazil, your bus will stop at the Argentine border and you will have your Passport stamped. Then the bus drives over the bridge and on the other side you have to stamp your entry to Brazil. The bus to the waterfalls is touristy and is waiting for you at the border.
Depending on the bus, it may be the case that the bus into the city simply continues and you have to wait for the next one. This is because the residents of Puerto Iguazu only have to go through control in Argentina, but not in Brazil if they return on the same day. As always, you never know how long it will take at the border. When I was there on the way to Brazil it tool less than 5 minutes at both controls. While when going back it took 30min at the Brazilian border.
Once you have arrived at the park, there is the option to buy tickets at the cash desk or with a credit card at the machine. I had bought it in 1min at the machine because the queue for the cashier had about 10min waiting time.
To start in the park you have to take an park internal bus. The waiting time can be very long here. I had to queue 1h on a weekday. Others I met reported over 2 hours waiting at the weekend. Others the day after me were lucky and were in the park in less than 10 minutes.
The bus will drive you to the start of the trail. On the way it will have an extra stop where you have to get off if you have booked a boat tour.
The trail starts directly with a great view of the waterfalls. It’s close to the river all the time, so that you get different views of the waterfalls almost all the time. After about 2km you come to the highlight. A footbridge leads right in front of the waterfalls and you get a unique view. Depending on the wind, it can be more or less wet here.
Finally, you go up a tower with an elevator. Here you have a great view again. Then you have reached the end of the park. If you want you can have something to eat here. Otherwise you have to queue up again for the internal bus to leave the park. Depending on the number of visitors, this can take quite a while, like at the beginning.
The trail itself takes about 2 hours. Due to the variable time at the entrance, the exit and the border, the time for the excursion can vary a lot. You can find information about the prices here: https://cataratasdoiguacu.com.br/