Instructions
Play through the game until you get to the eastern side of Mt. Mjolnir. Go all the way to the south to get the map to this area, and head back north and then west as far as possible. Walk south until you see a brown area just ahead of a bridge that is above you.
Travel up onto the hill on the right and then follow the path all the way north, east, south and then west. Following this path basically takes you in a circle, and it's impossible to get lost. Go up the hill to the north and then head east.
Walk north through a narrow passageway until you see another hill. Climb up the hill and cross the bridge to the east to find a blue circle leading to the west side of Mt. Mjolnir.
Go north to find the map for the western area of Mt. Mjolnir. Follow the path as it goes down the mountain in a spiral. The map for the western area of Mt. Mjolnir is simply the map for the eastern area that has been flipped upside down, so just follow the same path that you took on the eastern side but reverse the directions.
Follow the path until you reach another blue circle. Walk into the circle to enter the Mjolnir Dead Pit.