This is book number 2 in the Swallows and Amazons series.
The beautiful second volume in the cherished adventure series that the Guardian called "the 1930s equivalent of JK Rowling."
The Swallows and Amazons return to their lakeside home (in England's Lake District in the 1930s) bursting with grand schemes for the summer--camping, hiking, fishing and exploring. But a shipwreck and an impending visit from a Great-Aunt threaten to foil all their plans. Never fear: the discovery of a hidden valley and a secret cave lend new excitement to their days
The sequel to Swallows and Amazons, Swallowdale is charming and imaginative, yet firmly rooted in the reality of nature. Swallowdale will "capture the imagination of the Harry Potter generation" (Guardian) and will be treasured by generations to come.