The world of Sanctuary is never the same twice. That's because parts of Diablo III's environments (excepting towns, cities and some landmarks) are randomized. Like puzzle pieces, they fit together to form mazes and dungeons that can be different each time you play through the game.
Every time you start up a new game or load an existing character, the world changes. You'll find unfamiliar foes and unopened treasure chests in new places. What's more, the physical layout of areas can shift; locations of caves and ruins can move around, and the well-trod path you took earlier might be covered with monsters. Even quest objectives can move around!
Not all parts of the world will shift under your feet. Safe areas - like camps and towns - will remain unchanged. In these places, you'll find merchants to trade with and repair your gear. You'll also find your followers and other key NPCs (non-player characters) here. Select any of them to initiate a dialogue and ask for advice or learn about their histories.
In towns, you'll also see a magical emblem etched into the ground; identical emblems can be found elsewhere in the world. These are waypoints, arcane circles of teleportation scattered throughout Sanctuary, and you can use them to move between areas. When you discover a new waypoint in Campaign Mode, you'll be able to return there from any other waypoint you've previously unlocked. In Adventure Mode, you'll begin the game with all waypoints already unlocked.
Selecting a waypoint will open the Waypoint map, which displays each location you've discovered. The waypoint closest to your current quest objective in Campaign Mode will flash; when you're ready to progress the story, travel there.
Quests are the story of Diablo III and your battle against the Burning Hells.
You'll be able to see a full description of your current quest — including your objectives and where you should go next — in your quest log (PC: "J" key; Console: press BACK or SELECT, then navigate to the "Quests" section). Your journal will also keep a record of your journey — a bestiary of the enemies you've encountered, and a collection of books of lore you've collected.
Quests provide rewards of gold, experience, and items. Some quests have bonus objectives, optional tasks that can be worth extra experience and gold.
More often than not, quests will be given to you by your closest allies, but on occasion, you'll find that the world itself presents you with a path to tread, a foe to slay, or other "opportunities."
If you want to replay the game’s story mode, you can access the Reset Quests feature from the Game Settings Menu (PC). You will begin the campaign in Act I, and all of your quest progress (and waypoints) will be reset – quests must be completed and waypoints unlocked again as if you’re playing through the game for the first time. Quests you complete after this reset will grant extra rewards.
Though all act bosses drop guaranteed legendary items for characters of levels 1-59, when using the Reset Quests feature, the boss of act IV will drop a guaranteed legendary item for level 60 characters, and the boss of act V will drop a guaranteed legendary item for characters of levels 61-70.
As you travel the world of Sanctuary, you'll also come across events—small pieces of gameplay like miniature quests. When you encounter an event, the name of the event will appear on your screen along with its objectives.
Events are the demonic rituals, enemy ambushes, caves full of starved prisoners and other random occurrences that challenge you on your way through Diablo III's main storyline. They can offer different rewards, present different foes and even change their conditions from playthrough to playthrough.
Many events have the potential to offer bonus treasures.
Keywarden monsters have been sighted throughout the world of Sanctuary. Defeat these creatures and you may earn keys that — when used together — unlock a passage to a hidden pocket of the Burning Hells. Rumors hint that the Hells' most fiendish champions are cooperating in these tiny realms. When you invade their refuge and stand in triumph over these monstrosities, you may be able to harvest the fell pieces of their bodies, necrotic organs that can be used to forge legendary items of unparalleled power.
Diablo III's randomization supports replayability, but it also means that saving your progress is handled in a unique manner.
You don't have to manually save your game in order to pick up where you left off. Your game state (including experience you've gained, loot you've acquired, and quests you've completed) will be automatically saved as you progress and reach checkpoints. Your game is also saved when you're done playing and choose the "Leave Game" or "Exit Diablo III" options from the Game Menu. It's important to exit your game in this fashion (rather than simply turning off your PC or Console) in order to make certain your progress saves correctly.
If you ended your game in the middle of a dungeon or wilderness, you won't reappear there when you load your character. Instead, you'll appear at your last checkpoint, or in the closest safe location: usually a nearby town or camp. In order to return to the site of your last battle, you can run back, retracing your steps, or use a waypoint. Once you've unlocked a waypoint, you can then return to that area at any time, so they're very important anchors to your progress through the game.
You have the opportunity to explore as much or as little as you'd like to, but you should always search carefully and find waypoints to ensure that you can move efficiently through the game world.
When you enter a new area, you'll see a greyed-out, incomplete map of that space. As you travel through the area, you'll begin to fill in that map.
If you're lost, you can open your map (PC: "TAB"; Console keys: D-PAD down) to get a rough idea of your surroundings. Areas you haven't yet reached are blacked out until you explore them, at which point they'll fill in and you'll see the boundaries of the area in greater detail. If you see a pulsing circle on your map, head towards it; it indicates the location and direction of your current quest target.
On PC, you can also see the minimap, a smaller, zoomed-in version of your map, in the upper-right corner of your screen. This minimap is useful for quick navigation when you don't want to open your map.
Many different monsters lurk in Sanctuary, and they will try to kill you in diverse ways. Some will spit acid or beat hurricanes at you from afar; others will lunge, hoping to knock you back and rip you apart before you can react.
In addition to the massive variety of "normal" monsters roaming the land, you'll regularly come face-to-face with special monsters.
Champion monsters have their names displayed in blue. They travel in packs and are more powerful than regular monsters: they take more hits to kill, do more damage, and have abilities called affixes, which enable them to do things like teleport away from your attacks or unleash bolts of lightning when they're struck.
Rare monsters have their names displayed in yellow. Rare monsters have more Life than normal for their type, possess a special affix, and are usually surrounded by a pack of three to four minions who are weaker but possess similar abilities.
Unique monsters have their names displayed in purple. They're usually more powerful than champions: they have more health, do more damage, and often have multiple abilities.
Champion, rare and unique monsters give rewards commensurate to their increased difficulty: bigger health globes with greater healing power, more gold, and more (and often better) items.
At certain points in the game, you'll find yourself faced with truly frightening boss monsters: massive or otherwise extremely dangerous foes that overshadow all others. You will have to use all of your skill and cunning to defeat these monstrosities, and, if you're able to dispatch them, you'll earn tremendous rewards.
Below is a list of the monster affixes — unique monster powers — you're likely to encounter in Diablo III. Take note: