Ideas for writing my own riddle...?

In my English cl I have to write my own riddle and I'm not sure what to do it on. It has to be something tangible, like an animal or object, rather than something like love or the night. Basically, I have to describe whatever I choose as a topic and the reader has to guess what I am describing. Any ideas for a good topic and maybe examples of personification, metaphors, or similes I could use with that topic?