Windowless means having no windows at all. A windowless room has solid walls with no openings to let in natural light or fresh air. You might find windowless offices in the interior of large buildings, far from any outside walls. Some basement classrooms are windowless, relying entirely on electric lights.

Being in a windowless space can feel confining because you lose track of time and can't see what's happening outside. Without windows, you can't tell if it's sunny or rainy, morning or afternoon. Some people find windowless rooms uncomfortable because humans naturally prefer spaces with natural light and views of the outdoors.

Certain spaces are deliberately kept windowless for specific reasons. Museums sometimes use windowless galleries to protect delicate artwork from sunlight. Movie theaters are windowless so films can be shown in complete darkness. Secure facilities like bank vaults are windowless for safety. But most people prefer rooms with at least one window, which is why windowless apartments are usually cheaper and harder to rent.