I loved the Mu.dac. I found it by mistake while trying to find the history museum, and being…read moresomeone who loves design, decided to go in!
The staff were super friendly (and were willing to practice my French with me, even though it took a lot longer). I spent a couple hours, really looking at things (it's a small museum).
When I was there the first exhibit was on perspective, and the second was on touch- which was a shared exhibit with another museum! The touch one was really cool because you so rarely get to touch anything in a museum. Lots of different textures. I think one of my favorite exhibits was about a man who records himself everyday, then listens to the tape for that day a year later (and records over it).
The third floor was a glass exhibit, and it's always nice to look at glass.
I'd definitely go here if you're visiting Lausanne!