networking

That would depend on your goals.

If you want to play games with your neighbour, you could probably get away with two APs sitting in your windows. Heck, you might be lucky and a power line Ethernet could work.

If you’re a business and want both properties to be one network, with the speed and reliability that you would expect, then you would want a point-to-point system with directional antennas.

And if you wanted minimal interference, you would probably want to look at 60Ghz. E.g: https://mikrotik.com/product/wireless_wire

Check out https://arstechnica.com/gadgets/2021/08/point-to-point-wi-fi-bridging-between-buildings-the-cheap-and-easy-way/ which is a good article on how to do this

Ugh I forgot the product name, but Ubiquity has devices specifically for this kind of networking. You can get two nano things outside to bridge the network directly to a single machine or a switch. They also have bigger dishes for even longer distances, but the cheapest ones would be perfect for shooting across the street.

It would be more expensive than a router; but it would work way better than just doing a wifi bridge between two routers that weren't meant for that range or through both sets of walls

What you've described isn't a bad idea, but honestly if you're going across the street, just aligning some cantennas or using a proper point-to-point wireless ethernet setup will do the job perfectly fine - no need for additional routing unless you have a specific use case.

If you have line of sight, your best bet is a point-to-point wireless connection. Which can be accomplished with one router.

Edit: After reading the link I posted more closely, the cost estimates are quite high. You can buy everything you need ~$100-200.

I'm sorry OP, I don't have a solution, but I'm nosey. What's the situation? Why are you slinging access across a street?

Mikrotik wireless wire will get that done without needing two routers.

This is what dedicated AP are for, though if it will works sort of depend on distance and line of sight. Maybe you could setup a directional antenna to catch the signal on the other side with an AP or a repeater. You can also buy a bunch of APs and setup a mesh if the distance is not too great.

Is slinging an ethernet cable across the road from power/phone poles an option?

Are you getting 2 public IP addresses from your ISP? Do you intend to run different LANs for each property? Are you the wifi admin for both properties or do you intend for the tenants of the secondary to bring their own router+AP and hook up to an Ethernet drop from your network? It's kind of hard to make network recommendations without knowing the full context around how/who will be using these networks.

Even if you want them to be completely separate, you still only need 1 router as long as that router has multiple NICs or can vlan to whatever switch your wireless Ethernet bridges are connected to.

You might actually have better luck using a second router as a client on the other end. Routers will often have more/better radios.

I did this years ago with directional cantennas. The distance was about 350 feet or 106 meters. It worked OK but seemed easy to break.

I remember once being confused why the printer wasn’t working only to realize I had selected a printer a block away at someone else’s house…