I’ve written up a guide to Nightmare Rifts so you have an idea of where to go to obtain the lures and what’s the deal with the mechanics, stages and loot related to Nightmare Rifts. There’s even a neat Nightmare Rift Powerup Sheet that you can reference whilst you’re still getting used to what the powerups do.
Check out the full guide here: Guide: Nightmare Rifts.
RiftGrate 
probably the least “fun” part about the Nightmare Tide expansion are these rifts…..sigh.