How do you get Kanai's Cube?

I just loaded up the new patch and there doesn't seem to be much direction on how to actually acquire this key new item. Zultan Kulle talked about it briefly, and then I had no quests indicating where to go next.

How exactly do I acquire Kanai's Cube?

Solution 1:

Just teleport to the new zone, Sescheron Ruins (act III, Top Right corner of map) and explore. I found it in the Elder Sanctum map area.

Solution 2:

Along with Kanai's Cube, patch 2.3 also added the dungeon "Ruins of Sescheron". This dungeon appears around the Arreat Crater, in Act 3. You must be playing Adventure Mode.

If you clear the dungeon, you will gain access to the Tomb of King Kanai, where you will find Kanai's Cube.