I downloaded this app from the QR code on the (free) maps available in the visitor center. The are two walking tours in the free map. This app only covers one of the two. It was useful that they provide map support, but iPhone XS was seldom the exactly following the tour line making it a bit confusing. Also, the user interface is a bit clumsy as the map does not switch back to the tour waypoint description if you tap on a waypoint.