These ravens are located in Helheim and there are 6 in total.
Raven 1
Head straight from the entrance to Helheim to find the raven in middle of structure that holds the horn on the bridge.
Raven 2
Head straight from entrance following the bridge north until you reach an area filled with statues and souls. Before the next door, turn left and head down a side path, walking across the ledge. Once you emerge, head up the climbing wall to the left. Crawl to the top of the rock and climb left to find the way down to another level. Once at the bottom, swing to the right and look down. The raven will be flying around underneath the bridge.
Raven 3
Head straight from the entrance and follow the bridge north through the area filled with statues and souls. Crouch under the rock to proceed and climb up the wall straight ahead. Destroy the sap on the right to reveal the raven standing on the stone ledge above a chest.
Raven 4
From the previous raven head back down the wall and turn left. Follow the path past the helwind container. Climb up the stone steps to the north and turn east to shoot the red sap revealing the raven outside the hidden chamber.
Raven 5
From Raven 3, climb out of the pit using the north wall to find this raven straight ahead.
Raven 6
Head into the hidden chamber and take the elevator down. Head up the stairs on either side past the Mystic Gateway to find the raven top of an archway.
