I am large as a castle,yet lighter than air .100 men and their horses cannot move me.What am I?

a cloud

To find the answer to this riddle, let's break it down:

"I am large as a castle." This statement suggests that the object being described is significant in size, comparable to the size of a castle.

"Yet lighter than air." This means that despite its large size, the object is somehow lighter than air. This rules out any heavy objects like stones or metals.

"100 men and their horses cannot move me." This phrase indicates that the object is too heavy for a significant number of individuals, along with their horses, to move it. This eliminates options like vehicles, rocks, or any massive physical structure.

Putting these clues together, the answer to the riddle is "A shadow." A shadow is not a physical object but rather the absence of light caused by an object blocking sunlight. Shadows can appear large in size, yet they have no weight and cannot be moved by any physical force, no matter how many people or horses are involved.