The last of the 10x10 F-Series geomorphs (at least for a while) is F18, which is a large crack in the floor of a 40 foot by 30 foot room. The crack is directly above a 20 foot by 70 foot rectangular room on a lower level; if there's light in the room below, adventurers should be able to notice it. The crack at its largest is only a foot or two across and thus easily jumpable, but if the party stumbles into the room without light, they may trip and get a sprained ankle or even slip down and fall through (for the thin ones) or get wedged in waist high. Also, the GM can optionally decide whether the crack is still crumbling; the entire floor may collapse, particularly if a large party enters the room all at once. There are also two rooms arranged around an L-corridor in one corridor; GM's option as to which sub-level these two square rooms are on.
It doesn't look like I'll have the F-Series PDF available until later this week, because I still want to do at least eight borders and eight corners.