Bambi Meets Godzilla: Level 20 Duskbear vs. Level 51 mage
As soon as you reach level 20, you begin your adventures in the multi-player "dungeons." Often, the most difficult task you face is getting a team of four to go. It pays to be patient. Be prepared to wait at the entrance while you invite people to go adventuring with you. Often you'll find that people will join your team if you just wait a few minutes. Be sure to select the map for the dungeon you're going to, so that people will know where you're going; do this before you send an invitation to the whole world. It all starts with the Nether Forest.
Game play here is fairly straightforward. Just kill the monsters and grab the goodies.
Bambi Meets Godzilla: Level 20 Duskbear vs. Level 51 mage
(Please indulge me here. I did this photo tour, solo, with my level 51 mage on Server 8. Obviously, this is not a representative four-member adventuring party.)
The monsters you'll encounter, in order:
The Boss: Narosa, Son of Bloodfang
At level 20, it will take a few rounds to defeat Narosa, but you shouldn't have any problems getting throught the Nether Forest with a full team.
Narosa Has a Couple of Minions with Him
Narosa's buddies are more of a nuisance than a threat. If you come in with full rage, a couple of aoe* attacks ought to get rid of them.
*aoe = Area of Effect. That is, an attack that hits all enemies.