Lovely riverside Longridge is ground zero for activity days and high-thrills adventure birthday parties. On the banks of the Thames just outside Marlow, it offers a range of water and land activities (think kayaking, rowing, bushcraft) for all ages and abilities. My kids have been going since they were 8, and they are still massive fans. Tweens and teens can visit for the day, evening or camp out overnight under the stars. If your little Muddys are too young for tearing around without you, you can still kit them out in wellies and visit together for a waterside potter – keep an eye out, too, for school holiday organised sessions.