After ACT 3 Sceptre of God

I am currently in the Sceptre of God which I believe is the final act in ACT 3. I am on Normal Difficulty.
Can you continue the game on a more difficult level? Or is that the end.

There is normal, cruel and merciless. There are currently three acts. The plan is to have ten. Currently, you can do random maps once you reach merciless act three. The Scion class is unlocked in normal Sceptre of God. You find her in a cage if I'm not mistaken.

Thanks.
Do you automatically go to cruel or do you have to do something special.

After you defeat Dominus, a portal will open to the Twilight Strand in Cruel difficulty.