Answer: Mountains
Step-by-step explanation:
Shadow is always on the opposite side of the sun. This is because the sunlight is blocked by the body.
The rain shadow works in the same way. Moist air gets blocked by the mountain. A rain shadow is a dry area on the side of mountain which is opposite to the wind.
This shadow side is known as leeward side. the other side is known as the windward side.
This effect is known as the rainshadow effect which is associated with the mountains.