User blog comment:Gracey91/Achievements - By Smulder/@comment-92.29.115.194-20110921152629

An achievement for beating Hardcore mode with 4 or more friends, using only one world, and without the world having players that have played on other worlds before and without non-hardcore players. When all of the players have:

-Cleansed all Corruption -Crafted a combined 99 Hellstone Bar -Killed each boss once -Opened a combined 100 natural chests -Opened at least 2 natural chests in the Underworld -Opened at least 10 natural chests in the Dungeon -Opened at least 5 natural chests on Floating islands -Opened at least 10 natural chests in the Jungle -Opened the 2 ocean chests on each side of the world -Accumulated a combined HP of 1000 -defeated one Goblin Army -have housed one of each kind of NPC all at the same time

Without:

-Any characters that have been in other worlds or are not Hardcore entering the world, or any new characters entering the world after the end of the first day

Any cheats or glitches being exploited

Also:

-If you die, you don't get it, even if you remained in the world as a ghost upon it's completion. -The score keeper for this achievement is kept by the character, not the world. For example, if the player is present to mine 98 Hellstone bar but then leaves and all of the other players complete the objective, then the player who left won't get it until they are back in the world and another piece of Hellstone Bar is crafted. However, if the player is present to defeat King Slime, Eye of Cthulu and Eater of Worlds but is not present when Skeletron is defeated, it becomes impossible for that person to get the achievement in the current world. Therefore, the players hoping to get the achievement have to be in the game for each objective, and so cheating (entering the world at the start, leaving and joining in again at the end so the achievement is done for you by all of the other players in the game) is discouraged.

Basically you get an achievement for playing a world until the point where it usually gets boring, with friends and without dying.