Recently, the National Park system for Argentina www.parquesnacionales.gov.ar introduced an online purchase option for entrance tickets to one of the most popular parks in the world: Iguazu National Park (Parque Nacional Iguazu). The option to purchase online in advance represents a great step forward in convenience for park visitors. However, there are a few things to be aware of:
For now, the option only appears to be available in Spanish - but if you use a browser add-on for page translation or a simple translation web page you should have no problem.
In the center of a page you will see a horizontal row of clickable tabs - click on "Compra de Tickets" (Ticket purchase)
You should then click on "click aqui" - as marked below.
You will then land on a payment page, from where you can register using your Facebook or Google account, or create a new registration using your email address (Don't use a fake address as you will need to receive correspondence and a receipt). See below:
You will likely need to translate the subsequent pages to complete your purchase.
Once completed, be sure to print your receipt, which you will present at the dedicated window at the park entrance. The window is located to the right when facing the main entrance gate, and is marked "Ventas Web" (web sales). You will need to present proper ID (passport) for all adult members of your party and you will be issued standard tickets to be scanned at the entrance gate.
The process needs some adjustments - such as eliminating the need to obtain individual tickets upon arrival at the park, but it will save you some time and increase your piece of mind.
Additional tip: If you plan to visit the national park on the day following your initial visit, be sure to get your tickets stamped upon exit. This gives you a 50% discount on the entrance fee the next day - but you'll need to go through the standard ticket purchase process!