Will we see caves in asteroids?

It's something we've talked about. One of the things that we'll be looking at in the future is basically different cave archetypes. I think it depends on, obviously, the size of the asteroid, and can it hold something that would actually warrant a big enough cave or even creature to be in there. But I would love there to be... to be able to go out and explore those big caves and come into different creatures as well as different minerals and different challenges that obviously you could evade through those things versus crawling through them.