This seems ridiculous, but I cannot get the door open in the top right crypt in the Vale. It is the one with the special mechanism. I have a key with a skull on it called the Sanctum Key. What do I need to do?

Thank you!

You need the Gate Key to open that door. You can find it in the crypt that is located closest to the left on the Vale map. As for the Sanctum key, you need that later on to open a door inside Kresselak's Tomb.