Let's write!

Your characters are visiting an alien planet or some other place where the main inhabitants are not humanoid. (So, if you're set in the Lord of the Rings world, they could be visiting the eagles; elves, hobbits, dwaves, and orcs are all humanoid.) One of them sees an object and doesn't know what it is. Write a paragraph of what your character sees, describing the object to the reader.

The idea is to describe the object without telling the reader outright what it is or even giving them hints as to its purpose or use. What it turns out to be is for the rest of the story to reveal.