Artorias of the Abyss DLC

Dark Souls: Prepare To Die Edition contains the PC port of the critically acclaimed, console-based Dark Souls that thousands of PC gamers petitioned for. It features content also available for consoles via the Artorias of the Abyss DLC.

It has also been released as a full retail version which includes the original game as well as the additional Artorias of the Abyss DLC pack.

Prepare to Die Edition Wiki Sections

NEW CONTENT

Dark Souls: Prepare to Die Edition adds many hours of gameplay to the Dark Souls experience, which can vary from player to player.

The expansion introduces a new chapter called the Artorias of the Abyss, occurring after Sen's Fortress, in which the player must stop the spread of darkness within Lordran by defeating the Dark Knight Artorias.

This, of course, comes packed with a bunch of new things including:

New Bosses - Artorias of Abyss, Chimera of Tomb, and more
New Areas – Oolacile Tomb, Old Ruins and more
New Enemies – Abyss Guard, Chained Prisoner and more
New NPCs – Hawkeye Gough and more
New Weapons and Armor – Equip some from the new bosses, enemies, and NPCs
PVP Online Matchmaking System - Quick matching for co-op or PVP in an arena-style PvP

Accessing DLC

You do not have to complete the game to access the new DLC. However, you do have to complete a cryptic series of events to initiate the DLC event. Here are the things you need to do.

Clear the Hydra from the Darkroot Basin and save Dusk of Ooalice.
Obtain the Lord Vessel and give it to Kaathe or Frampt.
Go to the The Duke's Archives and kill the lone?Crystal golem after the bonfire. After doing so you will obtain the Broken pendant.
Now return back to where you killed the Hydra. Follow the water around the waterfall and you will find a black portal. Examine it and you will be in the Sanctuary Garden.