What kind of riddles are you looking for.
like When is a door not a door?
Or like "Something so hard that it can crush roofs yet must fear the sun"
or: I run, though I have no legs to be seen. I possess no heat, yet I do have steam. I have no voice to let words out, but from far away you can still hear me shout. What am I?
or even something like You hear it speak, for it has a hard tongue. But it cannot breathe, for it has not a lung. What is it?