In reply to arvinw:
I did the ones in Murren and Kandersteg recently. The Murren one is mostly a protected walk in the woods but has a few wonderfully exposed moments, as well as great views of the Eiger, Monch And Jungfrau. It goes downhill rather than up, which forces you to look down at the drop below! Took about 1h15, pre-breakfast (so there was no one else on it to get stuck behind). The one in Kandersteg is more challenging: quite steep in places and sustained exposure. It took us about 2.5 hours, followed by a long pleasant hike down (there is a cable car too).