There are actually two waterfalls called Giessenfall in the river Thur near Nesslau in the region Sankt Gallen, Switzerland. The waterfall upstream is called the Ober Giessenfall.
When driving from Vaduz (Liechtenstein) to Will the first waterfall you meet is the Ober Giessenfall. You can’t see the waterfall form the roadside but there is a red bench and a parking near the Ober Giessenfall (gps 47.211784, 9.217062). I am not sure if you can descend to the river at this spot. The Ober Giessenfall is a small waterfall.
Driving further to Will there is a small road/path going left. At the end there is a dam where the other small waterfalls are located.