A witch tower is kind of like a tall building where witches might live or work. It's usually made of bricks or stones and has a pointy top that looks like a cone or a hat. Like a castle, it might have thick walls and a door that only opens from the inside so that witches can be safe from enemies. But unlike a castle, which might have knights and soldiers to protect it, a witch tower is usually guarded by magic spells.
People used to believe that witches were real and that they could use their magic to do good or bad things. Some people thought that they needed to be kept away from the rest of the community to prevent them from doing harm. So, they built witch towers to keep witches inside and away from other people. Nowadays, most people don't believe that witches are real, so witch towers are more like storybook objects that make fun Halloween decorations or get used in movies and TV shows.