I was working Diessa Plateau in the North West corner in a quarry being attacked by the Dredge. The Dredge and their vehicles are popping up around the area and I’m working on an event to kill them. At one point, I think I was killing a vehicle when I suddenly fell through the world. I immediately hit Print Screen to capture the screen as I was falling.
I wandered around for several minutes taking pictures and trying to find a way back into the world. I was unable to get back into the world from below. After several minutes I took a nearby waypoint to return to the normal area of play.
I fell into water, so it looks as if the entire world is above water. Originally I fell into the lake and after a time I found a place where I could climb up a large sloping rock to under the terrain layer of the world. I was not able to climb through the terrain back into the world, however. As you can see in these pictures the terrain is invisible from below, so the only objects that area seen are the trees, plants and rocks, and even animals and mobs running around above.