well each block-group holds a list of "chunks" which are defined as rectangular groups of blocks, these are formed by an algorithm that searches through all blocks in the block-group. I run that algorithm if a block is added, or removed from the block-group. once the chunks are created, I assign simple scaled cube mesh's to the dimensions of each chunk (these meshes could have their textures scaled back to hide the effect - but i kept them to show a peek of whats going on. These chunks also have rectangular rigid bodies affiliated with them as well.
I should note that the stairs in this video is also a dynamic set of jointed rigid bodies even though it doesn't move much in the vid .