Access to the laboratory is via the safety gallery, which serves as a rescue shaft for the Mont Terri motorway tunnel. At a distance of ca. 1 km from the southern entrance we enter the Opalinus Clay Formation, Here it is very dry, whereas closer to the entrance there were puddles of water.

Inside the laboratory we find ourselves in a spacious and well-lit tunnel with 4 to 5 m height. Along the ca. 1200 m of tunnel there are almost 1000 boreholes in the walls, floors, and ceilings. On the one hand, these boreholes enable scientists to insert measuring instruments directly into the intact rock with a 300-m overload. They can, to a certain extent, simulate conditions that will prevail in a geological repository at a depth between 500 and 700 m. On the other hand, they can extract rock samples from the boreholes that can then be studied in international laboratories and universities.