Kalimdor Explorer

One of the easiest ways of tackling this achievement in as little time as possible, as an Alliance character, is to [url=http://wotlk.wowhead.com/?maps=457:611433602431594429573446581434563452545458534466525471515473505475496473489489492502492520490533487545461541474543453551450565450584452596449615450629450642453656466673476679485685484700479720477739475751461757430766410770402782420768441763449763]split the continent in half: the west side that is either only or easiest traveled by Darkshore/Darnassus's flight master and the east side that's easiest traveled by Ratchet/boat to Dustwallow/teleport from Shat to Hyjal (Keepers of Time rep necessary). While you could easily fly to almost anywhere on the map from a single flight master, this continent is plagued by painfully long flight times, especially along the west side.

You will find that you'll be missing a large portion of Durotar and Mulgore areas if you've never harassed Horde lowbies in those areas during your character's career. Both of these areas are easily accessed via Ratchet. Another area I noticed I was missing more than a few places was Thousand Needles which is more quickly accessed through Tanaris route, than Dustwallow Marsh.

Some passing tips about discovering Horde cities on this continent: Use Orgrimmar's side entrance, simply follow the eastern river in the Barrens all the way North. There are few guards and they barely dent a level 70 clothie. Thunder Bluff is easier, as you can simply jump on and off a well timed lift.

Good luck!

Guide to the 10 hardest zones in Kalimdor. Adapted to fit both Horde and Alliance.

Azshara
The only advice I can really give for Azshara is keep your morale up. Do not fall down the cliffs and do not let your patience break. This is the hardest zone in the achievement, but it is also my favorite.

Do not keep your mind stuck on the fact that you are getting slaughtered, focus on the beauty, it makes things go much quicker.

I came in from Talrendis Point (The flight path right next to Ashenvale) and worked my way to the end of the bottom half. I would suggest the same, as when you die on the bottom, it is a very long corpse-walk, and you are better off getting done what you can there in the beginning, then resurrect at the spirit healer and make your way from the beach (getting all the discoveries) and back to the bottom.

Silithus
An interesting zone, made hard by a few key points. The only way in is through Un'goro crater, and the only way in there is through Tanaris. And the only way into Tanaris (other than a very long swim) is through Thousand needles.

I renamed this place Bug-land after being here for all of a minute. Though the zone seems large, it isn't as it seems. All of the discoveries are very large, but for this one, roads can get a bit dangerous, because of an opposing faction known as the Twilight's Hammer. There is also world PvP here, so opposing players are a risk, especially at the bottom, near Ahn'Qiraj.

I came in through the path from Un'goro, and immediately discovered the two places right inside it. As, by now, you have MOST LIKELY, been through Tanaris and the Barrens, you have seen two different types of deserts. Now here is another. This desert seems more arid, lonely, and dare I say, hopeless.

I explored around the edges first, and then cut in at places to get discoveries. This method took much longer, but it was worth not getting destroyed by ever other aggro you get.

Edit: Sorry, may take a little while for me to fill in the rest.

Edit Edit: I'll keep this here for history's sake, though it is fairly out of date. I suppose Silithus still applies.

Level 40 Druid with no help, completed it.

For all you aspiring lowbies, here were my death zones.

-Azshara

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• Long Corpse-Walks, World boss, Close together mobs, Huge zone, Empty zone.
  
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-Silithus

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• Never found a place without mobs, World PvP makes it exceedingly hard, Twilight's hammer makes even roads dangerous.
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-Felwood

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• Only one general way to go, Large Zone, Many obtrusive figures blocking paths.
  
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-Winterspring

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• Only way in through is through a tunnel in northern felwood full of level 50+ mobs, Cliffs that can easily cause many deaths, Mobs with ranged attacks.
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-Ashenvale

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• Absolutely HUGE zone, World PvP, Hard to avoid Mobs, and they will team, Bough Shadow, places very out of the way.
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Now, of course, the first four are expected, but Ashenvale I was generally surprised about.

Being a druid, I had many tools other classes do not have available to them, and this made it much easier in the higher level zones.

I am alliance, so I didn't want to put anything in regarding faction, because I'm sure that you know for horde Teldrassil and Azuremyzt (+Bloodmyst) is no cakewalk.

Now, for Alliance, Orgrimmar at a lower level resulted in many deaths. The side entrance is by far your best bet, and while you're there, (Like I did) make a trip to Ragefire Chasm. And as always, guards... guard... the entrance to the mini-zone where the character starts out.

Also, in my next posts I am going to put down some directions for the zones I listed above, and some of the other ones which I thought were hard.