How far is the Iguazu National Park in Argentina from the cities?
The National park in Argentina is 18 km from Puerto Iguazu town in Argentina and 27 km from Foz do Iguassu city in Brazil. There are 3 ways to reach the park, by public bus, by taxi, by bike, by a tour company or using your own transportation. The price of the entrance fee of the park is changing according to the exchange rate. In Argentina, there are 3 different exchange rates. As on arrives at the park there are bots to buy the admission but one can also buy the advance ticket for the Iguazu National Park Argentina in this link. Price of the Iguazu National park fee in Argentina is around USD $25.00 per person. Children and local people pay less. 

For people that want to go back to the park the next day, there is a 50% discount on a second-day visit.

Walking around the Argentine side of the Iguazu Falls

If one is planning to do the boat ride, better plan a full day.

The Iguazu National park in Argentina is open daily from 8 to 6 p.m. 
At the entrance of the park, there is a kiosk for one to buy a key to drop their luggage (this is for backpackers). There are also maps in the park, like the one in the picture below. There are 3 train stations named CENTRAL, CATARATAS and GARGANTA. Arriving in the park one can walk to the Central Station to catch a train to Garganta Station (20 minutes ride). Instead of catching the train, one can go on foot to the other stations using the green trail (Sendero Verde in Spanish).  As arriving at the second station named CATARATAS, one can decide if catch the train or walk 1.5 miles on a dirt road to GARGANTA station. As arriving at Garganta station to reach Devil´s Throat (the highlight of Iguassu Falls) one need to walk on a metal bridge 3/4 of a mile long (1.100 meters).
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​The bridge is leading to the UNION waterfalls where is the border between Argentina and Brazil, locally know as devil´s throat. ​​

After seeing it one must walk back on the same bridge all the way to the GARGANTA train station and from there decide if take the train or walk back.  When the park is busy, people wait for more than 1 hour in line to catch the train. 

One must visit both sides of Iguazu Falls. Argentina side and Brazil side are wonderful, angles are different, perspective is different, light is different and the way people see them is also different. 
There are two national parks and the falls are in the middle, the Iguassu River is the border.  Se the Iguazu Falls location on the map. 

Best time to visit the Brazil side of Iguazu Falls? 
Some books mention that you that the best time is visiting the falls in the morning but in the winter-time, it is worth to visit it around mid-day. There is no much sunlight in the winter and also the sun is moving in a different way. As people arrive at the falls in Brazil, they spend like two hours to see it.  (07/29/2020)

It is a hard question to answer. The weather forecast in the last 10 years is changing and making it difficult to know the best time. What I´m going to do is making a list of information from different sources to help people plan their trip. 

This will help one to figure out about the four seasons we have in the southern hemisphere. Depends on the year dates will change. 
Spring starts on September 21 
Summer starts on December 21
Autumn starts on March 21
Winter starts on June 21

In 2020, in April and May the water level at the falls was low. It is not raining regularly as years ago. Commonly it would rain a lot in April and May and October, but in 2020 it was not happening. Depends on the year it can also rain a lot in May and June. Last time we lost the walkways at the falls was on June 8th, 2014, during a big flood. This year 2021, in April and May the water level at the falls was very low. June looks like a wet month. The water level is rising. 
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It can rain all year round, some months less or more. 
October can be the wettest month.
August can be the driest month.
The average amount of annual precipitation in Iguazu Falls is around 2000 mm (78 in)

Our Summer is very humid and hot, the average temperature is 31º C (88º  F)
Our Winter is not very cold, the average temperature is 17 º C (63º F)
The average year temperature is around 21º C (70º F)
​In the winter mornings can be cold but in the afternoon it warms up. 

70% of the days throughout the year are sunny.