Best practice to setup network between buildings

Heya reddit,

my company'll acquire a new building and it's my responsibility to set up the network there. As this is my first project to set up a network for two adjacent buildings I was asking myself what the best practice would be.

I already set up a lot of branch locations with IPSec and own subnets and routes and stuff, that's not the problem. And setting up the new building with an own subnet and connect it via IPSec to the main office is no sweat. But is that the best option? We'll probably get a dedicated internet connection for that building. Dark fiber to our main building is maybe possible, but I'm not sure about this. Is it even an good idea to get a dark fiber when we get a dedicated internet connection for the building?

We're using Juniper hardware if that's in any way important for some ideas/solutions.

I appreciate any advice or idea to set this up in the best way possible.

Cheers M3ph