The parallax has been built without any js or fixed positioning. It works on mobiles, but of course not with IE11.
To change the images, they have to be added as background images to the ID of each .section-image. As always in parallax, the images need to have more height than what is being displayed. The reason is, that the parallax needs 'something to play with' when the page is being scrolled.
The containers .section-text have a min-height of 50vh, but they can be filled with more content than that.
The holding container, .outside-container has to have its css added in the head box in the Element pane. If added directly in the Styles pane, the parallax effect will fail.
The village of Mittelberg / Monte di Mezzo. Mount Sciliar in the background
One of the many castles on the hills, along the Adige river
The Doge Palace to the right. The domes on the roof of St. Mark's Basilica behind it.
St. Mark's Square and Basilica