I accidentally did that in a projection room with a friend when I was aged about 10. We blocked up the projection hole but missed a bit. Turning round to the s

I accidentally did that in a projection room with a friend when I was aged about 10. We blocked up the projection hole but missed a bit. Turning round to the see the hall outside projected upside down on the back wall was one of the most magical bits of serendipitous learning I have ever experienced.