What can go up a chimney down, but cannot go down a chimney up?

Why this works

This riddle plays with the dual meanings of the word "up" and "down" in the context of an umbrella's position. When you say an umbrella can go "up a chimney down," it means that if the umbrella is closed (down), you can easily slide it up through the chimney. However, when the riddle states it cannot go "down a chimney up," it refers to an open umbrella (up), which would be too wide to fit through the chimney. The clever twist lies in how the positioning of the umbrella changes its ability to navigate the chimney!