What is as big as a castle. Weighs nothing, but a thousand men can't move it?

I would guess its shadow at the right time of night.

I keep saying stupid things...then correcting myself. Right time of DAY*

I think its a cloud....:-)

You're on the right track! The answer to the riddle "What is as big as a castle, weighs nothing, but a thousand men can't move it?" is actually a shadow. Shadows are typically as big as the object casting them, they don't have any weight since they are just the absence of light, and no matter how many people try to physically move a shadow, it will always be impossible because it is intangible and constantly changing with the movement of the light source.

So, in this case, the correct answer is the shadow. It's a clever riddle that makes you think about the nature of shadows and how they behave. Great job coming up with the possible answers of "cloud" and "right time of day" as well, as they can make for interesting alternative interpretations.