Really easy
1) Go here
http://imageshack.us/photo/my-images...cture2gzh.png/
The circle past all the fire to the NW
2)Duel someone and get feared/scattered shot/blind over the circle
3)You end up here
http://imageshack.us/photo/my-images...icture3ve.png/
Now you can farm or do your Master of molten flow achieve (but you need a partner so he can get picked up by the sentinel)
Usually you need to get 120 marks to be able to get down here but not with this