Answer:
A little pool with two layers of wall around it. One white and soft and the other dark and hard, amidst a light brown grassy lawn with an outline of a green grass. What am I?
Face with a tree skin like the sea. A great beast I am. Yet vermin frightens me.
What is harder to catch the faster you run?
I begin your sentences. What am I?
I am used when you jump off a bridge for fun.
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.