High in the hills, 31km from Yverdon-les-Bains, what appears to be a stereotypical Swiss chalet is the front for a Swiss Army bunker where troops were mobilised underground during WWII. Guided tours and a museum give an idea of what life was like for Swiss troops during the war that surrounded them, but which left Switzerland (relatively) untouched. Wear solid shoes and warm clothing as it's chilly inside.
You'll need to have your own wheels to get to the fort as there's no public transport.