The inner forces of the Earth meet with the outer ones, resulting in natural wonders. Once when we know the basics, we can point out the sites one by one.
Thingvellir are located in the middle, at the NS-axis of the polygon. The area is being pulled apart, creating a rift valley along the polygon from SW to NE, with the most appearent site where the polygon breaks due to shear stress as the polygon is also subject to some pressure turning it.
Around at the edges Reykholt, Deildartunga and Hraunfossar are found in the northern part of the Saga Circle. In the southern part are Hveragerði, Laugarvatn, Geysir and Gullfoss. Gullfoss has a 3 km gorge, ending at the line that passes through Geysir nearby. All those places have thereby a connection with the convection rolls grid, in this case just about one polygon.