There is an ancient invention. Still used in some parts of the world today. That allows people to see through walls. What is it?

Answer: windows

Windows are openings in walls that are typically made of glass or other transparent materials, and they allow people inside a building to see outside or vice versa. While windows may not be considered a high-tech invention, they have been in use for centuries and continue to be used worldwide for their practicality in providing natural light, ventilation, and a view through walls.