"mountain lair" ?
A mountain lair cunningly disguised as a flat river valley. Cunning !
https://www.google.nl/maps/place/European+Council+for+Nuclear+Research/@46.1152787,6.0460353,17356a,35y,37.48t/data=!3m1!1e3!4m5!3m4!1s0x0:0x81bef3ae7a885e31!8m2!3d46.2353713!4d6.0490803