"I am your largest organ and you wear me every day. I am waterproof, self-healing, and sensitive. I am the only organ visible to other people. What am I?"

Answer: Skin. Skin is the body's largest organ, covering about 2 square metres. It is waterproof, repairs itself after minor damage, and contains millions of nerve endings that detect touch, temperature, and pain. It is the only internal organ that others can see.