Snow and frost
When it gets really cold, frost crystals grow on the snow near streams. These crystals were growing in a hole in the snow, the stream was flowing underneath:
Snow covered the stream, with a few holes like this one. The snow was pretty deep, so I set up my tripod in the snow over this hole, in the narrow stream bed, holding my breath that the snow and ice underneath would hold the camera and tripod. It held, thankfully. I didn’t ruin the crystals by knocking snow in, which I’ve done many times.