Like many places in the Swiss Alps, there is really only stuff to do when the weather is nice. During our two-day stay there, we spent both days going to other cities because it was raining. I imagine the weather is much better in the winter, but of course the place would also be a lot busier. If you're planning activities, I would not book too far in advance, in case the weather is bad and you have to stay in.
Insider Tip:If you're not staying for too long, get a Swiss Pass and explore the country by train if the weather is bad. Over two rainy days in Interlaken, we went to Neuchatel one day and Italy the following day for free!