This is another picture taken with my new camera. The “cave” is above the big gray spot near the center of the mountain in the lower photo in the post above (did you follow all that?).
I think this looks like a cave, possibly a base camp shown on the official Mount Rainier site map. But a person in the Visitor Center said it is just a fluke of how the snow and ice have broken away and shifted, exposing a small portion of the mountain itself.
Color me skeptical.
Using binoculars (and even with the naked eye) you could see various places where there have been mini avalanches. Believe me, you are seeing a LOT of snow!