Be Childish:Think of the fun stuff your parents took you to do when you were driving them nuts inside the house. An arcade or even a roller skating rink (so retro!) is a much more fun indoor activity than sulking.
Try to be cultured:Find a random local performance that you probably didn’t even know was happening, a concert or a play or a comedy show, and snag the cheapest seats. You might discover a new favorite band, don’t care if it ends up being terrible, at least it will be dry.
Play photography:Indeed! Every fool can capture an attractive picture of a sunset on a clear evening, but snap a waterproof case on your phone and take some moody selfies or nature shots to be the Instagram-envy of all your friends.