Take the brown tunnel of the hub until you hit the end of it going west, then go north and follow that until you hit another fork in the tunnel that goes west. You'll hit a point in the tunnel where its under construction, and there's a nether fortress just south of it. I'll probably build a ladder down there eventually and put up some signing (if someone else didn't already).
Coordinates for the where the tunnel ends are approximately -800, 60, -396. If you look south from where the tunnel is, you should see some netherrack bricks and that's the fortress.
Something something chest near fountain.