Number Caverns is a free first-person 3D maths game for KS1 and KS2. Children explore a glowing crystal cave, collect number-crystals whose values add up to exactly the target, and carry them to the vault, which opens only on the exact total. Because the crystals add up to more than the target, the child must choose the right combination — building addition, number bonds and mental maths. No login, nothing uploaded, works on Chromebooks.