If you are looking not just for travel recommendations, but for suggestions that also take the time of year into account, this app is the one for you. The What's It Like app is currently in beta mode, and will help you figure out where to go as well as when to go.
For example, if you're trying to catch the Northern Lights in Norway, you best wait until December. Users will be able to input the dates they are hoping to travel and What's It Like will generate tons of travel recommendations for places that will have either a natural phenomenon for you to witness specifically during that time, or an alternate annual activity.
The app is accepting suggestions at this time.