Snow Cave

So, we have recently had so much freakin' snow, the kids decided to make a snow cave. The began the cave under the trampoline so they could have a nice, dry opening. They then began to dig out the cave. Well, the cave is about three feet in diameter wide, and six feet deep. The snow is as high as the trampoline and pretty solid since it's where we throw the snow we shovel from the side of the house. So far it has been a week and the tunnel/cave still exists. It's been fun for them to have a secret hideout. Even if itis cold. I have, however, ruled out them sleeping in it for fear it collapses on them.