Which of the 2 sentences is correct?
Sam is looking forward to see the Rocky mountains.
Sam is looking forward to seeing the Rocky mountains.
Which of the 2 sentences is correct?
Sam is looking forward to see the Rocky mountains.
Sam is looking forward to seeing the Rocky mountains.
In the example you gave, "to seeing" is correct. To understand why, let's think about different meanings of the word to.
By the way, the M in "Rocky Mountains" should be capitalized, it's part of the place name.