Praise the sun. Our Dark Souls Walkthrough provides tips for surviving the adventure, a guide to the entire world, and hints for slaying bosses.
The Duke's Archives
After you clear Anor Lando, you'll receive the Lordvessel from a character in a side room above where you defeat the boss combo in that area. You can head out of the main castle and along the side path to find a forest trail that leads to an opening. Without the Lordvessel, that doorway will be impenetrable, covered in an eerie orange light. With the vessel, you'll be able to enter the hallway beyond the doorway.
Past those boars, you'll find a larger chamber with a bonfire in plain view. Use it, then start forward again as you make your actual journey into the archives. At the top of the stairs, you'll step onto a platform and there's a lever you can pull. When you do so, a gate closes behind you as the platform rises. It's an elevator. Once it ascends one level, it'll stop and you can start forward again.
Your arrival on the upper level will not have gone unnoticed, naturally, so your first order of business is the group of guards that rush you. At first, you'll only see one or two, but don't let down your defenses. There are more lurking behind the pillars that line the edge of the room, plus an archer at the top of the stairs who will take potshots at you as you battle any of the lower troops. The battle that you wage through this area will go better for you, as usual, if you can lure a few enemies toward you (back to the elevator, for instance) and deal with them while their numbers are small and they'll have a harder time slicing or shooting you in the back.
Even when you reach the top of the short staircase, there are more guards to either side of the doorway and yet another archer ahead of you. Again, draw the weaker enemies down into the lower room and don't give them the chance to hit any harder than absolutely necessary. Progress here comes to the smart and cowardly soldier, not the brave one.
Through the archway beyond the large cluster of guards, there's a magic user. He will pelt you with magic from a distance if you let the guards distract you. It's doubly important here that you lure the guards into a safe area and dispatch of them so that you're not too distracted. The guards and sorcerer are both capable of hitting you hard, no matter how lengthy your life meter and no matter how high your defenses, but they're pretty weak if you're meeting their attacks with a capable shield instead of your exposed back.
Pushing past that first sorcerer, you'll soon find a second one who is positioned partway up a high staircase on the far side of the room. You have to put yourself out in the open to approach him unless you head along the left or right side of the room using bookcases and the underside of the stairwell for cover. You should do that anyway, to find the Large Soul of a Brave Warrior that is resting on a corpse beneath the stairs. Don't get careless, though; there's a chance when you rely on the architecture to shield you from the sorcerer that he'll get impatient and come to find you. If he does, it's easy to sneak up from behind and take care of him. You just don't want to give him the chance to do something similar to you.
When the area is clear, go ahead and start up the staircase. You'll note that it splits left and right near the top. You will find less resistance to the left, but to the right there's more of interest. Work your way through several more soldiers, using the architecture to your advantage as possible. You'll find an opening the the left where you can obtain the Twinkling Titanite from a corpse. When the main balcony ledge reaches a dead end at the chest, be careful because the chest is actually a Mimic monster. Defeat it to obtain the Crystal Knight Shield.
Now return to the top of the stairs you climbed a moment ago and this time head along the left route. You'll find an archer there, and past him along the balcony another piece of Twinkling Titanite, waiting in a chest. Grab the goods, then return to the top of the stairs yet again and head around toward the back side of that balcony.
You'll now find yourself on another of the lift elevators. Prepare yourself, then pull the lever. The elevator will ride up to an upper chamber and you can head along a branch to the right. This is a narrow corridor and mostly it just ascends along stairs. You should keep your shield ready, though, because partway up the stairs you'll have to battle a lizard enemy. It should be easy to defeat if you block its attacks and respond with melee attacks of your own. Then you can keep climbing.
As you continue your climb, you'll see one of the rare enemies that melts into the floor as you get near. Past it, the hallway begins to grow thick with crystals. These don't harm you, so just keep ascending and at the top of the stairs you'll find a mist-shrouded doorway.
When you pass through the doorway, you'll find yourself engaged in a boss battle with a fearsome beast known as Seath the Scaleless. Though he has a life meter, this is a battle that you cannot win. He's perched on a high ledge and will pelt you with dragon breath and crystals and all sorts of nastiness. You're expected to lose, and when you do you'll wake up in a crystal prison cell with your stats restored as if you just rested at a bonfire.
Look to the right and you'll see why that is: there's a bonfire. Use it if you like, then look around. Though he's hard to see through the crystal because he blends in with the architecture so well, there's a lizard guard posted just to the left of the cell door that was directly ahead of you as you appeared in the cell. You can attack him through the bars and then when he dies, you can pillage the Archive Tower Cell Key from his corpse. Use the key on the door.
When you step outside, a scene is triggered. Some lizards will run past you and to the left, where they'll ascend a ladder and climb to a high ledge in front of a locked door that you can't open yet. You should head to the right, in the direction from whence the lizards came.
As you descend the stairs in that direction, you'll find enemies climbing the stairs. They are easily taken care of with fire attacks, which leaves you free to explore the cells to the side of the trail (which the squid-like enemies will not enter). You won't find anything of interest until the third cell, which contains an enemy prisoner. If you drop through an opening, you'll find a corpse at a dead end. Check the corpse to find the Archive Prison Extra Key.
Head out through the nearby door, then continue your descent along the stairs toward the right. There will be plenty of the squid-like enemies along this route, but they're no real threat if you don't run out of fire attacks. Clear them out and as you reach the base of the area, you'll find yourself in a large, circular area. You can head to the right from there, through an opening, to find two more of the squid-like security detail. Defeat them and check the items that they drop for the Soothing Sunlight and Beautiful Sunlight miracles. There's a locked prison cell and prisoner nearby, as well, but you don't yet have the key.
Head back out into the circular area and look along the edge to find a ladder. You will need to climb that ladder and take care of some enemies that wait up top, so recover any health that you may have lost and then do so. Note that the guards attack with lightning-infused weapons, so you should make sure that you have a shield that's strong against that element. When you defeat the guards, you can deactivate the alarm that has been wailing ever since you first left your cell. Also check the nearby chest for the Archive Tower Giant Door Key.
With that key in hand, you've done everything you can in this area for now. Descend the ladder to the circular room at the base of this tower, then climb back up the stairs that you descended a moment ago. Return to the area where your sell was located, near the top of the tower, and keep climbing from there in the direction that you saw the lizards flee when you first broke out of your cell. You'll find the base of another ladder. Climb it, take out any lizards waiting at the top, then open the huge doors with your newest key.
If you want, you can take a detour here. Head left along the planking that leads left from the high platform at the top of the ladder. At the end of the planking, you can drop down (still hugging the wall) to a lower bit of planking. Continue along that area to find a cell you can enter to snag the Maiden Hood, the Maiden Robe, the Maiden Gloves, the Maiden Skirt and the White Seance Ring from a corpse. Now return to the high platform and pass through the doors.
Through those doors, you'll find yourself back in the more visitor-friendly portion of the archives. However, there are still plenty of enemies. As you start forward, you'll come to a 'T' in the path. There's an enemy waiting out of sight to the right (you may see his shadow), while to the left an archer waits along the path. Quickly tend to the enemy to your right, then head left toward the archer but be careful; there's an enemy hiding behind the door frame and he will try to attack you from behind as you deal with the archer. It's not a bad idea to dash so that you can rush the archer and roll around behind him, then take him out and the other sneaky enemy without having your back to either of them.
Continue forward, climb some stairs and then you're back in the area that looks like a massive library. As you start left along the walkway, you'll run into another of the sorcerers. Make sure that you block any spells on the approach, then take him out swiftly to minimize the damage he can inflict. You'll also have to worry about another sorcerer who tries to take you out from the other side of the room.
As you start past the nearest sorcerer, you'll see that you can continue straight ahead. Do so and continue along the balcony. Defeat any enemies you find (there won't be any serious threats) and watch for a staircase that ascends to the right. When you find it, start up the stairs to the first landing. Defeat the enemy, then turn the lever and you'll cause the staircase to spin a quarter-circle. When it finishes spinning, you can head up the stairs to defeat some enemies on an upper balcony.
Proceed left along that balcony and keep your shield ready. Further ahead, there's an enemy with a bow and arrows. Get close and kill him, then look around in the immediate vicinity. There's an opening in the railing to the left and if you look down, you'll see another of the staircase sets that can be spun. You'll have to drop through the opening now and aim so that you land on the stairs. Then climb to the first landing and turn the switch to turn the stairs. Once they finish their rotation, descend the stairs to reach a lower ledge.
Next go right a short distance and you'll find an opening leading to the left. Raise your shield and step through the opening. Ahead, there's an archer on the far side of a ledge. Take care of him with a projectile weapon or magic, then look around. There's a ladder here that you can descend to the lower floor, where you'll see a lever directly ahead of the base of the ladder. Go ahead and pull it to open some shelving so that you can easily backtrack to the beginning of this dungeon area.
You can enter the room just beyond the lever to find books strewn across a wooden floor. There's a single treasure chest that you can open to obtain the Blue Titanite Chunk. The other nearby room also has a chest out in the open, but it's actually a Mimic. If you attack and defeat him, he'll drop the Enchanted Falchion weapon. Check other chests in the same vicinity for the Archive Tower Giant Cell Key (which opens the locked door behind which you saw the prisoner as you were making your prison break) and the Six-Eyed Helm of the Channelers, the Robe of the Channelers, the Gauntlets of the Channelers and the Waistcloth of the Channelers in another chest. In an adjoining side room that's easy to miss, near that chest, you'll find another chest that you can loot for the precious Crystal Ember. Make sure that you don't miss it.
When you've finished looting, there's also a lever to pull in the same room that has the two treasure chests and Mimic. When you pull that lever, a staircase will sink into the floor and you can descend the stairs to reach an outside area (though first you should backtrack and free the prisoner so that you can learn crystal-based sorcery skills from him, if that's of interest to you). If you do backtrack to free him, which is easy to do by spinning just one staircase to easily give yourself a shortcut back to the prison area, make sure to grab the Fire Keeper Soul from the back of his cell, as well. You can never have enough of those. The prisoner will appear back in the area with all of the treasure chests, so he's not difficult to reach.
When you descend the stairs that you lowered in that area by pulling the lever, watch out for an enemy that will try to surprise you from behind them. You can also check a treasure chest to find twenty of the Prism Stone item. If you're ready, you can also pass through the mist-shrouded doorway on one side of the room to reach the aforementioned outside area, though you may want to backtrack through the area with all of the wooden floors and head back a short distance to find a bonfire on a ledge, now that you've created shortcuts throughout the area.
Once you do step through the mist-shrouded door, you'll appear in a grassy garden area. This place is densely populated by the crystal giant enemies like those you likely have encountered in the Valley of Drake. You can stop to fight them if you need good experience points, but they will sap your resources and you'll need those for the next area that you'll be exploring.
From where you arrive in the outdoor area, head left along some planking and descend a ladder to the grass. Then you can head forward from that planking, with the stone wall to your back and find a corpse over a small rise. If you investigate the corpse, you'll obtain the Crystalline Helm, Crystalline Armor, Crystalline Gauntlets and Crystalline Leggings. If you head to the far stone wall and then right from there, you can also find a Blue Titanite Chunk on another heavily-guarded corpse. Then you're done in this area and should descend downhill, taking out giants with fire attacks or careful melee warfare.
At the bottom of the grassy slope, a crystalline trail leads into the Crystal Cave area.