A:
Fractals are subsections of the dungeon Fractals of the Mist. The Fractals of the Mist is the only dungeon that has levels of difficulty that you unlock with each playthrough. Higher levels apply the condition “Agony” which can only be negated with Ascended gear, but eventually the agony can be too much for that as well. The dungeon is great because the difficulty scales up, it has a good variety of content and you get some good drops from it as well. It still follows the same 5-member party setup though, so not a raid.
As a story telling element the dungeon is REALLY cool. Essentially every Fractal is a random location in time and space that you are sent into to stabilize for researchers. You go to places such as freeing an enslaved Giant, battling the Jade Maw (A Lovecraftian monster), being a Charr during the Searing… pretty much any point in Tyrian history. They also periodically add new Fractals as a way for future players to experience some of the previous living world story.
http://wiki.guildwars2.com/wiki/Fractals_of_the_Mists
“The only lasting peace is the peace within your own soul.” ~Ventari
