Almost everyone is familiar with the term "Toblerone", which is the brand name of the triangle-shaped honey and nougat chocolate first manufactured by Tobler in 1908.

This trail has nothing to do with chocolate but rather with a line of anti-tank barriers (known as the Promenthouse fortification and named for the river which the line follows) consisting of 3000 large (14 tons each) triangle-shaped concrete blocks running North-South from Bassins to Lake Geneva near Nyon.

During the Second World War, when the Germans invaded the neutral countries of Norway and Belgium, Switzerland feared they would not remain immune to invasion and thus built the line to protect the western frontier near Geneva. It was a massive job building bunkers, fortresses, ramming in railway ties and bringing in and setting up the blocks, which the Swiss factories could not produce quickly enough so were brought in from France and Luxembourg as well.

This parade of concrete blocks so much resembles the chocolate, that the soldiers nicknamed them "Toblerones". The placement of the blocks is strategic: The 45-degree slope facing the enemy offers more resistance to bombardment, and a tank running up the slope is put off balance.

An interesting feature along the trail is a fortress called "The Villa Rose" which was built to look like a regular house but whose windows are fake (Trompe-L'Oeil) and whose walls are over two meters thick and housed massive cannons and other armaments, and was set up so that the soldiers could survive for weeks inside.

The trail itself is pleasant and easy to walk, mostly along the river and through forests, often winding in and out of the Toblerones. The main line of fortifications runs to the Villa Rose, and a bus stop near-by means the walk can end here, after 10 km.

Continuing on past the Golf Course to the Lake, then on a winding, wheel-chair accessible trail, you can walk through the Promenthouse Reserve to the National Museum in Pramangins, and on to the train station at Nyon.