Walk into a large hotel or office building and you may find yourself in a soaring open space with glass overhead and balconies ringing the sides. That is an atrium — a central hall that brings light and air deep into a building's interior. The Romans invented the form for their houses, but modern architects revived it for a different reason: daylight.

In a deep floor plate, offices far from windows feel like caves. An atrium solves this by carving out a vertical shaft through the building, letting sun reach lower floors and giving occupants a shared space to see and be seen. The glass roof keeps rain out while admitting light.

Atriums also serve as social condensers. People cross paths there. Cafes and seating cluster around the edges. Fire codes treat them carefully — smoke control and egress are major design challenges — but when done well, an atrium becomes the heart of a building.

Not every atrium works. Scale matters. Too small and it feels like a light well. Too large and it becomes an empty void.