Answer:
A little house full of meat, no door to go in and eat.
This is in a realm of true and in a realm false, but you experience me as you turn and toss.
Two bodies have I, though both joined in one. The more still I stand, the quicker I run.
I don't have eyes, but once I did see. Once I had thoughts, but now I'm white and empty.
I dig out tiny caves and store gold and silver in them. I also build bridges of silver and make crowns of gold. They are the smallest you could imagine. Sooner or later everybody needs my help. Yet many people are afraid to let me help them.
People take me on walks and I run and have fun. What am I?