The Famous Five Library Books 1 – 21 Collection Box Set by Enid Blyton:

The stories take place in the children’s school holidays after they have returned from their respective boarding schools. Each time they meet they get caught up in an adventure, often involving criminals or lost treasure. Sometimes the scene is set close to George’s family home at Kirrin Cottage in Dorset, such as the picturesque Kirrin Island, owned by George and her family in Kirrin Bay. George’s own home and various other houses the children visit or stay in are hundreds of years old and often contain secret passages or smugglers’ tunnels.