This mystery is located in the northern region of Snotinghamscire, just northeast of The Sleeping Jotun.
Where to Find Titanium for the Altar
To complete the mystery, you’ll need to offer 3 pieces of Titanum at the altar. You’ll most likely already have some of this in your inventory at this point in the game, but if not you’ll find plenty in various minor treasure chests and breakable ore deposits. The former can be found throughout the game world but are usually concentrated in settlements, and the latter are scattered throughout the landscape, but mostly in mountainous regions (such as Snotinghamscire!). Alternatively, if you’d rather not wait until you find some by chance, you can purchase Titanium from any Trader for 30 silver a piece.
Once you have 3x Titanium, make the offering to complete the mystery.