It may seem unbelievable but you can build houses out of plastic bottles filled with sand. These projects are made especially by NGOs from African countries. For example, the house from the video below was made by the Samaprman Foundation. The plastic bottles were gathered from trash cans and then filled with sand. This way, volunteers managed to make 6,000 `bricks` from sand-filled plastic bottles. With the help of these bricks they succeeded to build a small house which is used as a classroom. See more details in the video below.