This mystery is located in the southeast of Suthsexe, directly east of Crawleah. There are three entrances to the mine as you approach from the north. The correct entrance is the one on the right, facing south.
How to Find the Mysterious Cauldron Tablet
Once you’re inside the mine, head south to find a barricaded wall with a fire pot beside it. Shoot the fire pot to destroy the wall, then continue south through the mine until you reach what seems like a dead end. Face east here and look below you to find a hole in the wall. Go through here and move the barricade on the other side to the bottom of the ladder. You can then climb the ladder and turn south to continue through the mine to another ladder. This time you’ll need to shoot the link on the ladder to lower it, then jump to it and continue through the mine.
The path will be fairly linear from here until you reach a rope wire. Use this to reach another chamber with some fire pots and a barricaded wall to the south. Use the pot (throw it at the wall or place it nearby and shoot it) to destroy the barricade, then go down the slope to find an inscription on the wall, indicating how you can find the tablet. In this chamber, head to the south and jump in the water here. As you swim eastward you’ll need to smash through a wooden barricade. Keep swimming and the water will eventually lead to a chamber where you’ll find the Mysterious Cauldron Tablet.
To exit the cave, take one of the fire pots and throw it at the nearby barricade. The path will lead you outside eventually.