The Grimsel Test Site (GTS) is located at an altitude of 1730 metres in the granitic rock of the Aar Massif in central Switzerland. It lies at a depth of around 450 metres beneath the surface and is reached by an access tunnel belonging to the Kraftwerke Oberhasli AG (KWO), the local hydro-power company.

The GTS tunnel system is around one kilometre long and was excavated in 1983 using a full-face tunnelling machine (diameter 3.5m). The Test Site offers ideal conditions for carrying out a wide range of test programmes. (Please see the Visit Grimsel section for details on visiting the GTS.)

Tunnel Layout

Main project locations are shown below.