I think playing a card game or board game is fun. Drinking wine and conversating about some wild philisophical ideas. Watching a film and discussing it later, or during the film. These are just some ideas I can think ok while inside...oh wait, How about cooking up something special, that requires a group effort, like making home made dumplings?
If your outside, and the weather is warm enough and raining, I say, go on a nice muddy hike. I love doing that!