Answer:
This thing all things devours: Birds, beasts, trees, flowers; Gnaws iron, bites steel; Grinds hard stones to meal; Slays king, ruins town, And beats high mountains down.
Hard to catch, easy to hold. Can't be seen, unless it's cold
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.
The man who made it didn't need it. The man who bought it didn't use it. The man who used it didn't want it.
What's a place you have left but didn't enter?
People take me on walks and I run and have fun. What am I?