Its a world format which is generally used for First Person Shooters - because it adapts the world to only show a "visible" set of polygons meaning you can budget more polygons on the worlds and such
it also has some other fancy features like built in collision, lightmapping, entities (thanks to GuyS plugin above), generic world format used by a multitude of editors which come as free or purchaseable - and if used in alot of current game
and i'm not sure what you mean solid like a matrix
Tsu'va Oni Ni Jyuuko Fiori Sei Tau!
One block follows the suit ... the whole suit of blocks is the path ... what have you found?