Welcome CharlesD

The reason to why we can control the dream and do impossible things without realizing that it is a dream, is because of an decrease of the aminergic system of the brain that governs critical thinking.
Although just like we with intent can move our arm, we can also with intent control these systems. It's truly a mystery how that is possible, although isn't free will a mystery in itself?

When we intend to become aware of our dreams the system magically, just as easily as the movement of an arm, just increase and we become aware that we are dreaming.
In the later morning it is easier to become lucid because of the increase of this system, although my point is that this system can be increased within the dream and even in the earlier stages of sleep with just intent, which is a very beautiful thing However this is just an interesting theory, but it can be useful to know about. ^-^

About your recurring dream An easy definition of dreams is that they are our subconscious, memories and emotions. So in other words dreams is an experience of our own personality!
So it is very symbolic and only you can interpret your dreams. If I would make a guess I would say that the dream about corridors seems like a pattern of repetition, perhaps you felt like something in your life was always remaining the same and every decision you made led to the same end. But then some day something changed and you were free, the symbolism of trees and the sky can be freedom.

Lucid dreaming is a good way to both understand your personality and yourself, and if you want you can learn to change your personality and therefore your life by realizing where you want to make changes.

I hope you feel welcomed and if you ever need any help with your practise, well you are in the right place

Sweet dreams and enjoy your stay.