Instead of simply inserting one "event" after the other ("you walk through this nighmarish labyrinth as you...") offer them "intersections" from time to, possibly with some hints where there next decision might take them. After some Perception roles, perhabs!
Hopefully, this creates a "feel" of a labyrinth, even if without "a map". Tried the "event after event" approach in a different down-hive-mission (of my own) and the feeling failed miserably
[ENCOUNTER]: The Chasm of broken ways (Vault-Level)
The tunnel/way the pc are following ends in a large, cylindric chamber criss-crossed by gangways and pipes (similiar to what is described in the Encounter given in TF). The bottom lies in darkness an can not be seen. If the pc drop something to "gauge" the dept...it turns out to be really deap and ending on soldi ground. The gangway leading from the side of pc has collapsed, leaving only a downward bend "stumpf" of the forma bridge on both the opposing sides.
If the pc want to cross the chasm, they have to cross the distance (about 10meters or more) "layway" along the pipes criss-crossing the the room. Ask for extended outine checks for strenght to get across or for check on acrobatic for balancing along a pipe... or brachiating among them like a monkey!
Anyway... after the first made it safe to the other side and the second, voices and the sound of approaching men can be heared. A slaver patrol!
The pc have to hurry (worsen the checks or put a limit to the number of roles allowed). If the pc are fast enough, they can disappear without being seen. If not, they might have to fight the patrol while being on different sides of the chamber (or even in the middle of crossing it!). Take a number of three to five slavers, as you see fit. Raise an alarm if the pc do not get out of the way or can´t deal with them quickly.
[ENCOUNTER]: Flood Pipe (Vault-Level)
The pc opened a heavy door in a wall or the ground which leads into a large and damp pipe (3m in diameter) filled by half with a dirty-brown water. Due to the smell obivously part of some sewage system. The pipe obivously goes upward in a steady angle, the sewage flows down slowly. Smaller opening along the sides lead in more sewage
As the pc walk the pipe, after a view hours can first make them run across some rat-size leach-like creatures trying to attach to them. INT to notice that removing this suckers while inside the sewage is a sure way of getting a nasty wound infection, properbly resulting in the loss of limbs if not treated with the next day!
Anyway, as they walk upwards, mention the water begins to rise notible and that the current gets stronger. Ask every checks for strenght and later swimming to go a long, one worse then the other. If the pc want to leave, there are opening hatches, but they are hard to open while "rusted shut / seized up". At the end, the water does not rise farer the "need-to-swim", but the current is strong enough for challenging swim tests. (Contest between the "strenght" of the pipe flow and the swimming pc) if they do not get out at one point, they will be flushed down in THE DEEP SINKS.
[ENCOUNTER]: The fungid devil and THE DEEP SINKS (Deep Level)
A large room (30m x 60 m) filled with sewage (do not even THINK to dive to the ground), the walls covered with some green shroom-like goo glowing in a sick and pale yellow-green that as floating in patches ontop the sewage as well. Advances are going round the walls every ten meters, with "Sewage Level X m" written next to it. Each one of them rarely broad enough for a man to stand on, but solid rokcrete. The next ("Sewage Level 60meters"). is 2 meter above the sewage actual sewage level. There are iron steps in the center of two of the walls leading up. Large pipe opening in the ceiling can be visible for every pc
The stench is overwhelming! Have every pc make ordinary checks for Toughness. If they do not succeed, they are quiet nauseated and dizzy (-10). Three level of failure, and they pass out! (Hopefully, the other pc notice and dive for them!)
As the pc move along the walls (or swim, if they fell in!) they might register something moving in the water... and see a fate yellow-green-glow growing stronger! After a while, a huge semi-plant-like massive blobb emerges, obviously made up of the same material then this goo all over the place. The blobb will start to ooze up the the vertical walls (!) after the pc, extending many small tendrils as it does so.
Make a point about that it does not leave the water completely, seemingly just "stretching" itself ..and the glow beneath the sewage growing stronger!
Make this a "flee!" encounter with a massive opponent. Perhaps you want the pc to be ablte to spot something like "nerve clusters" in the blobb, allowing to "stun" it with pain for a round of time if hit. Decide how much success the pc need in "climbing" to reach the next door out of this (and what it takes to open it!).
If one pc dies and burns a fate point, "pull the plug". Literally. Make a sound of MASSIVE machinery below be heared... and the sound of a flush... the sewage and the thing go down gurgling...and the glow with it, leaving the pc in utter darkness till the get to a door next to the stair (glowing EXIT sign?)
(No stats given for the "fungid devil in the DEEP SINKS"...but are they needed at all?)