I just used the tool for 5min and after clicking on an area to see its breakdown, the only way to get back seems to be via the breadcrumb navigation. That is a bit annoying. There could be a button somehwere to go one level up again. And ideally you would write to the browser history to capture when the user clicks the browser's back button or uses the back button on their mouse, which is what I did intuitively and then got annoyed when each time I did it I ended up on the landing page with "Zur Visualisierung" again :D