How to reach Crypt of Decay
Crypt of Decay is in the northeastern portion of the Plane of Tranquility inside of a cave. You'll find the entrance to this cave on the hill top - enter it and follow the windy path down until you reach the large glowing object which is shown in the map above.
Click the object and you're inside CoD! If you still need a bit of assistance finding this place take a look at my map below for an exact location of where this glowing pillar can be found.
Once you're inside CoD the way to zone out might not be entirely obvious to you either. In the northeastern portion of the room you enter the zone in you'll notice a weird rock-shaped object which is shown in the picture below. Click on this rock to zone out.