I did this in my bedroom about 3 years ago. I lived in a basement apartment and my bedroom had windows on only one wall. I used black posterboard and wedged it into the window frame. I didn’t want to use anything permanent since I was only renting. I cut an opening and used a large magnifying glass for the lense. I remember waking up the next sunny morning and there on the wall was a moving picture of the yard and street upside down on my wall. I was so excited, I wanted to run outside and invite people in to see the scene. I didn’t, though. After that, I experimented with holding a white piece of paper closer to the whole and moving the paper from side to side so I could see different scenes. It was great fun. When I took down the posterboard, I made a small camera obscura from an old computer paper box. I used the same lense and the posterboard to keep out as much light as possible. I still have it. It’s cool to stand in a dark room and point it towards a light room or outside.