I have decided to develop the concept I have already presented in the first part of the contest. The base was built in the clouds and was invaded some time ago.
Here my story is that the player is returning to the same base again after a while, so he knows the location more or less. I have designed a speed run where the player has to escape the approaching danger rather than get to the end as soon as possible.
So, the player starts at the platform at the very bottom. He has a chance to look around, but one step towards the ladder triggers the water rise (it is possible to see around 0:26 time mark). My idea was to have a deadly cloud of chemicals or smth instead of the water plus I wanted to make a countdown timer but got lost in the dark wood of blueprints. Anyway. The trigger event is marked with a crashing sound, it is possible to hear it on the video.
Then the player must run all the way up to the evac point on the lab rooftop. And because the player is supposed to know the location more or less already, it is not so frustrating to search for the way out. Plus I leave the hints such as lights and blocked paths. I have experimented a lot with the water-rising speed so it will not leave too much room to mingle around, but also not too little to break the keyboard.

Few details:
Late evening and low lighting so the guiding lights can be seen better. Blue light shows the path, and the green light indicates moving objects.
Other things I would consider if making it a real level would be to make sure the player is informed about what is going to happen, countdown, and immediate auto finish once a player reaches the rooftop.