The screenshot (showing Llyn Ogwen, Cwm Idwal and the Nant Ffrancon valley, where Yr12 are headed on Wednesday) was taken with the overlay set to semi-transparent so you can see clearly how the terrain links to the contours on the map...
Aneki.com also has a wealth of facts, figures and superlatives, and there is a handy little tool to compare two countries. Get exploring!

