To freeview stereographs such as these, all you need to do is slightly cross your eyes. You should then see one fully saturated image in the middle and one faint one either side. The middle image will be blurred, but if you “allow” your focus to drift, it will (sometimes quite suddenly) snap into focus and this middle image will be in 3D.
This all requires that your visual system de-couples two of its distance-finding mechanisms: eye convergence (cross-eyedness) and lens focus. Once you have become used to how it feels you will be able to do it very easily. Some peope seem unable to do it at all. Ever. And this includes my wife.
One tip: the further you get away from the image the less your eyes have to cross and so the less your focussing has to de-couple… and therefore the easier it is. Start a long way from the screen using the thumbnails, let it happen, and then click through to the enlargements..
Now, with a triptych you will see two 3D images in the middle. If you drag your eyes one more level of crossedness you then see one 3D with enhanced 3D effect. Or you can just look the image as a triptych, with each component having a slightly different perspective.