Steve
I live in Iguassu (Brazil), borders with Ciudad del Este (Paraguay) and Puerto Iguazu (Argentina).
This is the only region in the world which you can pass by three countries driving only 8 minutes.
Of course, as I am Brazilian, I don´t need to show my passport when I enter Paraguay or Argentina. To enter Paraguay I don´t need to show anything and to enter argentina, I just need to keep all windows open and let my driver´s license on the dashboard, visible from outside. Sometimes (rarely) I neet to stop and open the trunk.
Yesterday night I went to Argentina. Gasoline is up to 80% cheaper and their supermarkets are amazing.
I just left my office here in Paraguay, went home to take my best friend with me because she wanted to go to the supermarket and exactly 20 minutes after I left my office, I parked in front of the supermarket in Argentina... Easy, isn´t it?