What do I do with my friends for fun?

Now that it's summer (well as 'summer' as it can get in the UK) I've been lounging around bored out of my mind. I got plans to meet up with friends but we have no idea what to do on the day, something that doesn't require money or a lot of it.

We've talked about going to town, the beach and many more places outdoor but it'll rain. Although the forecast could change. And indoor stuff just don't appeal to any of us cuz we've already been couped up in our houses for almost 4 weeks already. Though we could have a game night or smth.

Just please recommend me some activities so I don't die of boredom!