This mystery can be found in the west of Hamtunscire, just northeast of Chepeham, AC Valhalla. You’ll find Wocig, a cave, already noted on the map.
How to Find the Mysterious Coat Tablet
As you may have already guessed from the mystery icon, this is another hunt for a mysterious tablet. You’ll find the entrance to the cave as you face northwest toward the mystery location. Enter the cave and continue into the main chamber, where you’ll find a rowing boat waiting. Use the boat to row north and then west through the cave, then north again. At this point you’ll find some minor treasure on a ledge above you to the northwest. Loot this and then jump back down to the boat.
You’ll find that you won’t be able to row anymore, with stalagmites blocking the way forward. Instead, you’ll need to swim to a ledge marked by white stone to the north. As you face the ledge, turn northeast toward it and then run up the rubble to grab onto it. If you don’t grab it first time, you’ll fall back down into the water, but keep at it and you’ll soon be on the ledge. Once you’re atop it, turn southeast, prompting Eivor to comment on the challenge ahead. You’ll find an inscription on some stone here, and a hole in the wall to the east.
Once you’ve read the inscription, go through the hole in the wall to the east. Through here you’ll find the tablet in a locked room to the east, and two barricades blocking the way to the south. You won’t be able to move these from this side, so instead you’ll need to turn north and go through the open doorway opposite. In this room you’ll find a bunch of explosive fire pots. Shoot the pots near to the small hole in the wall to the east, then get out of the room as the rest explode. You’ll be safest on the other side of the locked gate near the tablet as the explosions continue.
Once all the fire pots have exploded, you can go through the hole and take the Mysterious Coat Tablet.