Surely as hell I'm not the first person to discover this but I can't see it listed on github so I'm reporting it here just in case and it's going to bother me if I don't. Please let me know if this is documented.
Game world: Cabbage
Description: The dividers between the different quadrants of the place the runecraft altars teleport you to can just be walked over. As long as you enter from an altar that doesn't have its own untraversable terrain, you can run all over the place and even walk right up to the unreleased altars. This gives me a strong sense of "I shouldn't be here" and may lead to additional strange behaviour involving smuggling combat gear onto Entrana or something to do with wherever the hell the death and blood altars are connected to. I don't know, I didn't stick around to experiment with that.