That’s called an intranet (which is like the internet but for a building or small area).
The internet isn’t really anything more than computers connected to other computers. If you want to make your own internet you can connect two computers whether wired or wireless, and voila. You can host a website locally that only those two computers can access.
See also: !selfhosting@slrpnk.net
While you were out there whacking your straight stick, I spent years studying the blade…