Lake Lucerne is really nice. When the weather is good, you can see the snow-capped mountains. Unfortunately, we stayed there for three days, and the weather was good only when we arrived in the evening of the first day, so we didn't take advantage of it.
The buildings by the lake, the Ferris wheel, and the Flower Bridge Water Tower are simply too beautiful to take in. The boat ride to Weggis is even more beautiful.