An igloo is a dome-shaped shelter built from blocks of packed snow, traditionally made by Inuit people of the Arctic.

The design is surprisingly clever: builders cut snow into large blocks and arrange them in a rising spiral, each block leaning slightly inward until they meet at the top. The entrance sits below the main floor and features a tunnel, which traps cold air and keeps warmer air inside. Body heat and sometimes a small oil lamp can raise the temperature inside to a comfortable level, even when it's freezing outside.

While many Inuit people today live in modern homes, igloos were once essential winter shelters, particularly for hunters traveling across the frozen landscape. An experienced builder could construct a small igloo in under an hour using only a snow knife.

The dome shape is key to an igloo's strength: the weight of the snow blocks presses them together, making the structure surprisingly sturdy. Snow also insulates well because it traps air between its crystals. These same principles appear in other architecture: domed buildings everywhere rely on similar physics to support heavy weight without collapsing.