You can even set up your own DNS and create your own domain names for said websites.

Don't you need at least AS numbers and BGP (or equivalent multiple independent networks) for it to be an "inter"net?

I've read a creepy pasta somewhere from this guy's pov, that somehow discovered a computer at one of the businesses they took over as a contracted IT, think car wash or something, and they've ended up discovering a computer in a closet that was networked with other computers in the area to share CSAM and other smut. I forgot how the story ended as it was fairly long, but they were describing the technical non-sophistication of the whole network in great detail. The PCs were basically just networked windows xp workstations or something, without any sort of password protection on them or their shared folders.

OK. Now how to make a floppy drive?

Or a LAN. Could do a WAN which itself can be interconnected over a wide area. Usually by routing over the internet but you could use something like satellite uplink or miles of dedicated cables.

But the interconnection of multiple LANS and WANS is what would make an “internet”.

So maybe 2 universities joining their own networks would be moving towards a private “internet” but I think we’d still call that a private network or a WAN.

It’s interesting to consider where the definitions change.

In fact, forget the internet!

Do the Elders know you have this?!

This could have been a really interesting question if OP hadn't been so vague. As is, there's too many interpretations to answer. Do they mean the physical connections? The protocols and services like IP, DNS and BGP? The world wide web, with its sites, links and search engines?

Does OP consider the Dark Web its own internet? Or a large corporate network its own internet? What about self-hosting a huge number of services in your own home?

You need two entire networks.

So yeah, take two computers, set them on different networks, bridge them via router.

Connect them directly via wifi.

Nitpicking here, but unless there are multiple sites, that's just a LAN (local area network), and even across multiple sites without certain other bits and pieces, it's still "only" a WAN (wide area network).

Admittedly, the latter can be called an internet (lowercase i important). The LAN would be an intranet.

To replace the Internet (capital-i and all) you'd need, at the very least, a DNS server of some sort, if not reimplementation of any tools that assume IANA and ICANN are at the top of the hierarchy (or successfully lying to them about where those roots are on the network).

To head off the question of where VPNs fit into all of this: Any or all of this could be implemented over a VPN that uses the existing capital-I Internet to transfer data, at the expense of some bandwidth.

Some care would be needed to not let data leak onto the real Internet at any of the end points, but it could be done. This is basically what TOR does for the Dark Web.

I was going to make a joke that you didn't even mention the tubes, but TIL that's anti-net-neutrality idiot propaganda :( Idk why I thought it was, like, Tim Burners Lee or someone trying to explain things to non-nerds.

Check Lora Radio mesh. It’s kinda what you describe.

I mean you could have an open wifi mesh and/or a network of either cheap fibre/ethernet with open switches. Then using OSPF or a similar routing protocol that supports routing over LAN networks you could handle the routing between all the remote networks.

I think you'd need to break the network up at some points to break down the broadcast domains. You could do a similar thing to defederating, by not accepting certain routes, or routes from certain OSPF nodes.

Issues with LANs that get too big without splitting into a new LAN (limiting broadcast domains) and definitely even the most modern wifi becomes problematic with a number of active stations online (wifi is half duplex in operation). So multiple channels and some backbone either over point to point radio links, or cable to connect wifi zones and alternate channels would improve things somewhat.

Not sure why you'd want to do something like this. But the tech to do it is fairly inexpensive.