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 Great Hollow
At the bottom of Blighttown, there's a bonfire in a stone passage built into the side of a mountain. Head out of that area and toward the edge of the swamp water, then hang a left. Proceed past the are that leads up to Blighttown's higher level and keep going, then cross through some swamp water to a low point where a huge tree limb allows you to ascend toward a tree.
Climb the bark trail and you'll reach a small cave that contains the Plank Shield. You'll find it on a corpse. Look left to the wall and you can hit it with your sword to make it dissolve. Head along the trail that you reveal to find a treasure chest that you can open for the Twin Humanities item. Grab it, then hit the wall behind the chest with your weapon to make it dissolve.
Head along that trail and you'll see the name of The Great Hollow flash on the screen as you descend a barren trail that leads to the top of a ladder.
Climb down the ladder and continue along the path. As the path widens and you see huge tree roots ahead of you, there's a bonfire that you can light. Then it's time to see about descending through the area along the huge roots.
Head slightly left and start down the trail. You can descend for a long way without encountering anything, save an empty room along the right side of the path. Continue past that chamber and you can drop down to a lower branch and head forward. There, you'll find a corpse. Investigate to obtain a Titanite Chunk. If you look down from there, you'll see another corpse and (to its left) an room with a gray floor. Sitting in that room is one of the chameleon creatures with buggy eyes that inhabits this area (they look like the cursed frogs in the Depths).
If you wait for a bit, the creature may spy you. It will head up along the branches, which is what you want. Watch carefully, as it is capable of climbing to a higher ledge and then dropping down behind you. Hit it with a fire attack if you have one to keep a safe distance. When you're ready, you can drop down to the lower ledge but know that there are two more of the same creature waiting behind the wooden wall where they're harder to see. They will rush you if they spot you and you need to tend to them quickly without getting caught up in their cursing mist attack. If you're playing through this portion of the stage online, note that you'll sometimes see strange images appear for a moment, like petrified statues. Those images let you know that other players are trying to proceed through the same area and are dying after being cursed. This is a very dangerous portion of the stage.
After defeating the creatures, investigate the corpse lying along the outer side of that lower room to find a Large Soul of a Nameless Soldier. Then head out along the nearby limb and look down to where more limbs crisscross on the way down. You can worry about grabbing items along those limbs if you like. You'll find the Red Titanite Chunk along one branch and the White Titanite Chunk along another. Lower down, there's also a Blue Titanite Chunk.
Keep descending by carefully dropping down along branches. As you head down through the tree, look around for another gray ledge extending from the side of the tree. It has a ladder descending from its side. You can drop down to that ledge from a higher branch nearby, then descend the ladder to reach another ledge with the gray, thatched surface. Look from there and you'll see another ladder descending to a wide area. If you start down the ladder, though, you'll attract the attention of a chameleon. You may prefer to drop down from a higher ledge with your weapon drawn and kill the chameleon upon arriving on the lower level. There are others in the same vicinity, though, so be ready to hit them from a distance to avoid being cursed.
Circle around the area and look for a hole in the floor, near the trunk. There's a ladder along the side of one such hole, but that's not the one for which you are searching. The one you want to find provides a view of a corpse resting on a limb. You can drop down on that corprse from above and investigate to find the Blue Titanite Chunk. However, there are more of the cursed critters nearby and they'll probably notice you and attack. Make sure that you avoid them.
Continuing down the tree, you'll soon find an area of red fungus platforms that extend from the tree. These are past the last of the cursed frogs, and they are inhabited by shroom enemies. The shroom enemies have good defense but you can easily block their attacks and let the fight drag on as long as it needs to. Just be careful that you don't let them mob you. Often, you can run past the shrooms as you drop along the final few ledges and reach the bottom of the tree. There, you'll find an opening that branches off to the side and reaches a mist-shrouded door. When you pass through that door, you'll start along a ledge that serves as the entrance to a new area: Ash Lake.
Keep in mind that Ash Lake is a dead-end region. When you're done there, you'll have to ascend back through The Great Hollow. All of the enemies regenerate and there are less options for movement going up than there were going down. It can be difficult to find your path, so we'll provide a few notes below.
First, head up through the chamber while climbing on mushroom ledges and avoiding the mushroom critters that run around throughout the area. As you ascend higher, you'll leave behind the reddish ledges and start making your way along tree bark. You'll probably encounter a cursed frog there before reaching high ground, which has a thatched appearance. Here, there are a bunch of frogs. Take care of them and keep circling around to find a ladder. Climb the ladder.
From the top of that ladder, quickly circle around. There are at least two more of the frogs and you want to fight them one at a time if possible. Then along the edge of the area, against a wooden wall, you'll find another ladder. Climb it to a higher ledge and walk forward another few steps from there to find and climb another ladder. At the top of that ladder, look around and you'll see a wooden limb nearby. Start ascending along that limb and you'll find a low ledge that doesn't even come up to your knees. It prevents you from traveling further, but you can turn your back to it and then backstep to hop up onto the higher ledge.
Continue ascending along the wooden ledges and you'll soon reach a cave area with more of the frogs. They are dangerous now, as always, but you should be able to fight them one at a time by luring them toward you. After defeating them, climb the ledge that they were guarding to reach a higher tree limb, then walk along that limb to find still more limbs that you can climb along. There are no more enemies here, just branches that crackle and break out of your way as you ascend.
When you reach the top of those branches, you'll find the bonfire that you found when first entering the area from the Blighttown. Rest there and then be on your way.