You must visit Zoltun Kulle in New Tristram, Hidden Camp, Bastion’s Keep Stronghold, or The Survivor’s Enclave in Adventure Mode in order to acquire the Kanai’s Cube. You will find that he will be quite pleased to show you the way.
In the meantime, Season Journey is a new feature. A player can approach a new season in a different manner and the developers wanted to celebrate individual player’s successes. In the start of season 4, you can track your own personal progress using the Season Journey Interface.
A Season’s Journey of a player consists of various chapters and these come with their own descriptive goals as well as achievements. As you keep progressing through the Season Journey, the milestones keep getting more difficult and a player belonging to any level will face certain challenges. Once Season 4 starts, this new feature will be made available.
There are several other significant features and changes that have been introduced with the latest update. For example, the various Nephalem Rifts will not need any Keystones. At the same time, The Realm of Trials has been removed from this game.
You will find that Generic Greater Rift Keystones now drop at any difficulty level. You will find all of this and much more officially mentioned in the Battle.net patch notes.
Stay tuned for more updates on Diablo 3!