No, not a cave but a part of a building; actually the building of Rausu Visitor Center. The dark area on the image is the upper part of a glass window. The snow pile there almost reached the roof and thickness of the snow on the roof is sizeable. Icicles' formed from the snow/ice mass on the roof, reaching the snow pile below at certain spots. Judging by the color and layers, it looks like there was more compressed ice mass underneath and than snow on the top. I just hope that the roof doesn't collapse..... I have not seen something like that in real life until then.