After you defeat the Iron Golem on the roof of Sen’s Fortress, you’ll discover a ring of light. Investigating it will summon a trio of Batwing Demons that will carry you to the city of Anor Londo.
There’s a lot going on here — you’ll be facing some really tough enemies, several mimics, some confusing floor plans, and the hardest boss fight yet. There isn’t much crafting material to find in Anor Londo, but what you’ll find is rare — Demon Titanite and Twinkling Titanite. You’ll also find a few heavy armor sets and some powerful, heavy weapons.
There is a choke point on the left side of the map that we should address. You can’t just walk through the front door of Anor Londo’s castle. You’ll have to detour around to the right along some narrow walkways. As you get close to the castle (and foolishly get your hopes up), you’ll encounter two Silver Knights wielding Dragonslayer Greatbows. They will knock you off of the narrow walkways with their powerful arrows or just block your progress. There’s no other way around them, though, so keep at it. Making sure you’re not weighed down will let you roll out of the way of their arrows. Alternately, you can equip gear with high poise so they aren’t able to knock you back as easily. Once you get close to the archer on the right, parry and kill him quickly so you can get inside the castle and visit the bonfire and finally breathe again.
There are several NPCs in Anor Londo. You’ll find Solaire of Astora (Praise the Sun!) by the bonfire inside the castle. Nearby, Siegmeyer of Catarina is trapped on a balcony by some silver knights. On the other side of the castle, you’ll meet the Giant Blacksmith. Once you defeat Ornstein and Smough, you’ll find Gwynevere who will give you the Lordvessel which allows you to warp between bonfires you’ve visited. After you’ve visited the Catacombs and found the Darkmoon Seance Ring, you’ll be able to return to Anor Londo and meet Gwynevere’s brother, Gwyndolin.
From Anor Londo, you can continue on to the Duke’s Archives or visit the optional area, the Painted World of Ariamis. To get to the Painted World, you’ll first need to return to the Undead Asylum and retrieve the Peculiar Doll.