While on the highway crawl to our family reunion dinner, we passed this strange structure. Are you wondering if that grey building is a house. It is a house but not for humans. If you enlarge the photo, you can barely make out the tiny holes in the concrete wall. This is a bird nesting house for swiftlets that make edible nests with their saliva. It is a traditional Chinese delicacy that enhances general health. More infomation about birds nest listed here.