Where is Northrend?
Northrend is the area in World of Warcraft that was opened when the expansion Wrath of the Lich King was introduced. You will see it on your map above and centered between Kalmidor and The Eastern Kingdom.
Why Go To Northrend?
Northrend is where you will spend most of your time once you hit 68 till level 80, so it would be a good idea to get there as soon as you can to speed up your leveling and to get access to the upgraded gear and if for nothing else to have a change in scenery.
Horde Paths to Northrend
The areas for Horde players are the same general areas as those for the alliance, but not the same docks. So to get to Borean Tundra take the zeppelin from Ogrimmar, you will land across the zone at a different dock than the alliance, but be in the same area for quests, etc… If you prefer to get to Howling Fjord then take the zeppelin from Undercity, again you will have access to the same quest chains as the alliance, but be in a slightly different area.
Borean Tundra To Howling Fjord Without Flightpaths
You can find a tusker village on the coast that will have a giant turtle harbored for you to ride from Borean Tundra to Howling Fjord and vice versa one to the other, there will be a short stop in Dragonblight where you can switch turtles. This is free and is similar to riding the boats, it would be a good idea to open up flight paths on both ends of the ride as well as running in when in Dragonblight to find the flight master.