Suggestions to lose weight?

okay well i want to lose about 20-30 pounds. i was wondering if there was some way to keep losing weight steadily before summer(which would need to be indoors cuz it's like 22 degrees out right now). Me and my best friend want to lose weight over the summer (even tho she doesn't really need to) I wanted to also know some good ways for outdoors that's fun besides swimming. Thx :D