Wintergrasp is the only non instanced full battle ground in all of World of Warcraft. It is nestled between the mountains of Icecrown, Sholizar Basin and the Dragon Blight on the continent of North Rend. The rules for Wintergrasp access have recently changed. The zone has changed from passive blockading of low level characters to an active expulsion. When the zone switches to an active battleground everyone under level 75 is expelled to a place in the mountains of ice crown.
Although there are restrictions on the battle for Wintergrasp now, the zone itself is still accessible in between battles. There are flight points for both factions and vendors with a handful of items even a level 1 can use. These items usually require stone keeper shards so would have to be purchased by a high enough level alternate character on your account. The best time to go to Wintergrasp is about 10 minutes after your faction wins it because most of the combat has died down and you will be able to run around the fortress a bit longer before an 80 notices you.
Now to get to Wintergrasp at a low level you might as well just run there dead. It may seem like a dumb idea, but by running there dead you avoid all the monsters and enemies. You can resurrect in Wintergrasp via the Battleground Spirit Guide without additional penalty and you will remain in Wintergrasp. You will know that you are standing near your factions spirit guide because aside from mouse over labeling, they will pop up a confirmation box with a time between 1 and 30 seconds to automatically resurrect.
The path to take depends on your race partly. Starting with humans you just go down to Storm Wind harbor and jump on the ship to Valiance Keep. From Valiance Keep you run north through Borean Tundra towards Sholizar Basin. If you die just stay dead and finish the trip as a ghost. Part of the trip requires you to be dead. You have to be a ghost to use the spectral flying mount to cross the mountains into Wintergrasp. Go through the pass into Sholizar Basin and continue north to the very top of Sholizar Basin. If you are west of the Avalanche then head east until you can access the snow covered slope that will allow you to walk over the mountains. If you are not dead when you arrive at the Avalanche you need to kill yourself. Make sure you are not in the Avalanche when you die because you are automatically resurrected and prevented from corpse hopping up the slope. As a ghost run up the Avalanche until you near the crest of the mountain and you will suddenly find yourself riding a spectral flying mount. This is how you get into Wintergrasp itself.
While riding the spectral mount fly east until you reach Icecrown Citidel then head south towards Wintergrasp Fortress. There is a small pavilion in the back of the fortress with a spirit guide in it. The pavilion is what you are aiming for. as soon as you cross from Icecrown into Wintergrasp you will lose your gryphon so make sure you hit the fortress or your in for a lot more walking. If you make the descent properly and are at the spirit guide simply wait 30 seconds right next to him and you will be resurrected and have full run of the fortress whether the walls are up or not. He is located roughly at the center of the back wall of Wintergrasp Fortress. If you missed the fortress you will need to walk to one of the other spirit guides for your faction. The grave yards change hands with whoever controls Wintergrasp so if you are on the winning team along with the fortress you should be able to use all but the opposing factions landing camp graveyard. just right click any spirit guide of your faction and ask him to guide you to the fortress graveyard and you will be able to get in that way. If you can’t figure out how to get up to the spirit guides look for the pillar of light near them. It is a ghost transporter.
For all other alliance races you will only have to take a boat or tram to Storm Wind and pick up the human path from there. For the horde, you need to take the zeppelin system to Borean Tundra then head north mirroring the human path from there.