International Tripoints are points where three country borders meet. There are 176 across the globe (according to Wikipedia) and this picture shows one of them.
In the cool of the morning light, it was a lovely place for Roger to visit whilst Hilary was reading in bed.
In the foreground is Argentina, to the back left Paraguay, and to the back right Brazil. Below is the convergence of the Rivers Parana and Iguacu. On the skyline – in the far distance – you can just see the skyscrapers of Cuidad del Este.