Before they were commonplace and comprised 99% of Worlds... Black-Boxes were but mere rocks that spanned the sizes of pebbles to boulders. That was until the Age of Connectivity, an age which sought about the beginning of Characterkind. The Black-Box came in many different forms shapes and sizes but now under the Dedos Administration, they all resemble the same modern rectangle shape. Many laws were brought in place to maintain this uniform design which controversially destroyed many Black-Box centric cultures... oh well I guess. The blueprints of the Blackbox aren't generally available to the public but history gives us a good jist on how they're all made.
Before the Black-Boxes dominated, the way to connect and disconnect from world's involved a proceess in which you transported connection-fluid in a jar and promptly smashed it against the rock to transport out of the world. You can still smash jars against the Black-Boxes to get the same effect but you would get arrested by Dedos for vandalism and destruction of property. This only works thanks to the Blackrock coating, now you can just stick your Paw-Pad into the machine and fiddle with all sorts of forumboards banks and the such. It's pretty hard to effectively destroy one of these boxes and in Public-Worlds they are generally very very safe-guarded, a destruction of Black-Box would endanger every life inside the World.