This section only includes people and locations required for the main quests in the game. If you're looking for information on class or guild specific quests, then check the Guild Quests section.
1 - Skuldoon
See the Skuldoon section (under Demigoth Lands) for details.
2 - Moon Bridge
3 - Staroxia's Tower
If you climb up the stairs to the top of the tower, you should run into Staroxia, once the Celestine of the Celestial Order and now just a simple "seer of the stars." If her name sounds familiar but you don't know why, it's because Emmindor suggested that you find her and ask her about the Relics of Power, but for some reason the game didn't give you a quest to do so.
Staroxia will tell you several useful things:
After the Shadow Ruins
If you're playing the Collector's Edition, then after completing the Shadow Ruins, if you return to Staroxia, she should give you the dialogue option "shadow amulet." (If she doesn't, then make sure you've identified the amulet, which you should have found when Nauselom died. You might also need to check your quest log.) When you ask Staroxia about the amulet, she'll offer you the shadow lord class, provided that you have a third tier class slot available.
The shadow lord quest involves returning to the Isle of the Damned (where you picked up the shadow stone required for entry into the Shadow Ruins). There you'll need to defeat a dracolich. A dracolich is basically the same as a fire drake, except that it'll shoot ice at you rather than flames. There are probably various ways of defeating the dracolich, but we just cast "cataclysm" twice, and that was that.
After defeating the dracolich, when you return to Staroxia, she'll reward you with the shadow lord class, and you'll gain the shadow lord skill, which is the only invokable skill in the game. Shadow lords, for some reason, do not receive a heraldry bonus.
4 - Naga Temple
See the Naga Temple sections for details.
5 - Altar of Runes
6 - Sleth's Safehouse
The door to the safehouse is locked, and you won't be able to get inside unless you go on a quest for the Guild of Mystery. See the Guild Quests section for details.
7 - Worglaw
Worglaw is a shopkeeper. Among other things, he sells the useful voodoo charm, which gives 5% protection against everything.
Worglaw is also the keeper of the totem of the tree. If you tell Worglaw that you need the totem, then he'll offer to sell it to you. Possibly, having a high merchant skill or a high honor attribute will cause Worlgaw to lower his price, but we've always had to pay 10,000 gold to get the totem from him. You can use the totem to get past the Guardians of the Forest (in the Demigoth Lands) and reach the Isle of the Damned.
If your character is more on the chaotic side, then you can also kill Worglaw and steal the totem of the tree from him. But if you do that, then you'll have to fight the Guardians of the Forest when you reach them.
If you're playing the Collector's Edition, then Worglaw will have quite a bit of company with him in his village, including thrall fighters and spellcasters, and spirits o' the forest. If you attack Worglaw to get the totem of the tree, then all those extra characters will turn hostile towards you, making for a pretty difficult fight. The good news is that if Worglaw and his pals like you, then they'll help you kill things. That's very useful, especially when you go up against Big Bad Mog.
8 - Shrine of Celestial Power
The shrine is used in a quest for the Celestial Order. See the Guild Quests section for details.
9 - Council of Stones
Like the Guardians of the Forest in the Northlands, the Council of Stones won't let you pass until you can tell them the password. You'll get the password "irynthabl" from Vartugg in Skuldoon (#1) after you've completed his quest to acquire his eye, and after you've placed four relics in the Chamber of Spirits in Talendor. Then when you tell the password to the council, they'll part, allowing you to enter the Black Swamp.
Note: Only two of the stone heads will "light up" when you approach. You'll have to talk to the one on the left. If the game doesn't allow this, move away to the west for a few seconds. Then when you return, interact with the stone head while it is talking to you, and you should be able to talk to it.
10 - Irynthabl Maze
See the Irynthabl Maze sections for details.
11 - Big Bad Mog's Safehouse (Collector's Edition)
The safehouse is involved in a quest from Maloke Brane in Skuldoon (#1).
12 - Giant Copper Scorpion (Collector's Edition)
When you approach this spot, you'll be attacked by a giant copper scorpion, plus some regular scorpions. The giant scorpion won't drop anything interesting when it dies, but you'll gain about 150,000 experience from killing it.