Shadowfang Keep

Easy achievement to get at higher levels. The instance is mostly linear, so you're pretty much just running forward. Below are the steps to getting the achievement.

Zone in to the instance.
Walk in, turn right.
Follow the path around to Rethilgore. Open the 2nd (middle) cage.
Talk to Ashcrombe. Ask him to open the courtyard door.
Run down in to the courtyard and to the far right side. Follow the curvy ramp off to the side up.
Run through all the rooms. This is linear.
You'll come to a dip in the stairs with some stairs to the left. Keep going straight past the stairs.
You'll come to Commander Springvale. Kill or ignore, run straight in to next room. You'll be outside on top of the keep.
Keep running straight and you'll arrive at Odo. Kill him or not.
Run out the other side back outside. Keep following the path. There's really nowhere else you can go.
You'll get a tower with stairs going down to some pens. Follow that down and back up the other side to another tower that leads up to Fenrus.
Kill Fenrus. Kill the voidwalkers with a bit of AoE.
Gate will open, run up.
Kill Wolf Master Nandos. Door will open.
Kill Archmage Arugal.
Fin.

SPOILER

History is going further, Arugal is dead, ressed by San'Layns and brought to Grizzly hills, dead again. He is changed for Godfrey and probably all bosses inside are changed for other. DM also revamped and there aren't same bosses like before cause of events in Westfall and death of Edwin. Edwin is changed for his daughter: Vanessa Vancleef.

This is an excellent guide, thank you very much