How deep is the sea? Pipkin the inquisitive penguin wants to know just that. With the help of a friendly seal, a big blue whale and a salty sea dog in a yellow submarine, Pipkin learns that the sea is very deep indeed! A VERY long poster (1.6 x 0.2m) at the back of the book shows just how deep the sea is - and how far Pipkin would have to travel to get so deep. A delightful sequel to Pipkin's adventures in 'How big is a million?' and “How High is the Sky?”