While it would have been great if someone thought to put conduit between structures when they were built, you can’t now, or it’s more trouble than it’s worth for some reason?
Doing it with a trench, conduit, and fiber is the gold standard solution. Over a span of decades, it’s definite the lowest total cost of ownership, and well as being the highest performance option as a bonus.
This guide is for the person who can’t trench for some reason. If you can’t trench, then your next best option is a wireless bridge.
A wireless bridge is a pair of directional antennas designed to be pointed at each other directly and stationary mounted. Because of this focused antenna, the range is far greater than any omnidirectional wireless signal like a normal WiFi Access Point puts out, especially the higher you can mount them.
If you have Line of Sight without obstructions, these nanostations work well.
If you need to punch through trees or other obstructions, you may need something a little more drastic, like a Yagi antenna setup.
Ubiquiti also has products for this sort of use. A Rocket M900 plus a Yagi Antenna gives you the best for of odds for that sort of use case
Once you have your bridge equipment chosen, there are a few other things to consider with the rest of your setup.
The Rest of the Network
Logically speaking, a wireless bridge can be treated like a very fancy Ethernet cable in terms of planning out the rest of your network.
Obviously you need something to take that ethernet output from your bridge on the Out Building side and plug it into a switch, so you can then start plugging in local devices for service. It’s usually a good idea to add a local wireless access point to broadcast from the outbuilding, as well as plugging in anything you can directly with ethernet for reliability and performance’s sake.
You will want to consider a PoE switch on both sides of your connection, to power your bridge equipment, as well as local Access Points and/or PoE cameras.
Unifi 60w PoE switches have 8 ports in total with 4 PoE ports for a max of 60w of power. Models with more ports and hire total wattage are available for those that need it, but most people will probably get by with either a 60w or 150w 8 port switch.
A Note About Cabling
Be sure to use outdoor rated cabling when you mount your bridge equipment. Standard stuff is meant for indoor use and won’t last long in the sun and weather. It costs more, but it’s for these reasons. Don’t ignore this or you will be rewiring stuff in a year or two.