Switzerland was neutral in WW1 but being neutral had not helped Belgium. Switzerland was the point at which the Western Front had to end. The nearest Swiss town of any significance is Bonfol, in the canton of Jura. It is not mountainous as the Alpine areas of Switzerland are, but it is quite hilly and not as easily marched through as Belgium.
However the Swiss were mindful of Belgium and had no intention of being used as a side door for either side to bypass the Western Front. They did not build trenches of their own, but they did build a chain of strong points and station a large force of their militia soldiers in the area, ready to fight if their soil was violated.
The building in the foreground of the third image is a Swiss Army fortified position. The ruined building beyond it is a farmhouse on French territory, in the no man's land between the two trenches. The fence posts in between are a simple barbed wire fence and it marked the frontier.
The fourth image is from the inside of the trench system (I dont know which army's trench) and looking south. The flag marks the end of the line. It was there for the benefit of new boys so they would know not to direct their fire beyond that point.