Four layers of one planet for children aged 6 to 8, hosted by Lupe, a golden retriever puppy who discovers everything alongside the child. The course goes in the one direction a child can never look: down. The cross-section that opens every episode is the same cut of the Earth with one more band lit, so the child always knows where they are before a word is spoken, and every depth is measured against the only ruler they always have to hand — themselves, stacked head to foot, going down. The crust is about thirty kilometres deep: twenty-five thousand children, and it is the thinnest of the four. Its top metre is soil, and that single metre is where every tree, every flower and all the food in the world comes from. A volcano is a window into the layer below, and its lava comes from a pocket five kilometres down rather than from the centre of the Earth — a correction the course makes on purpose, because it is the commonest thing children are told wrongly. The crust itself is cracked into plates a hundred kilometres thick that drift at the speed of a fingernail growing, and in Iceland there is a crack between two of them you can walk into with a plate on each side. The mantle is 2,900 kilometres of solid rock that flows like very cold honey — never a sea of lava. Below it the planet turns to metal: melted iron on the outside, and at the centre a hard ball at nearly the heat of the Sun's surface, solid only because the whole planet squeezes it. That melted metal makes the Earth a magnet, which points every compass and paints the aurora green. And the last measurement is the humbling one: the deepest cave anyone has descended is 2,212 metres and the deepest hole ever drilled is twelve kilometres, so nobody has ever left the skin. Every layer is shown with a real photograph, and there are no exercises inside the videos and nothing to get wrong.