Kyurem - Unaccessable?

I finally got to Kyurem's area, but there's a rock blocking to the lake where he freezes everything (I think).What are the requirements to get to Kyurem? I beat the E4 and have the national dex.I'm playing pokemon white, btw.

I've had this problem too, it's a pretty confusing place as I also ragequit on finding the ''freeze'' spot.
But trust me, the entrace to that little lake is really there. Search it thoroughly.