So,
The engineers told me that the submarine was only good down to 900m. It's just that the engineers never noticed that I was taking the submarine to a world where physics followed no such equation. I told them I could dive however far down I wanted!

"I bet you, I can take your stupid submarine even deeper than the Mariana Trench!"
"You should be asleep, ma'am."
"Shut up, you... but what do you think I'll find down there?"
"Parties, cake, and candy. Now please step off of the submarine."

I told them that I'd make it all the way down there for the parties, cake, candy. And they challenged my logic. They said I would be taking their most expensive creation yet - a high-tech attack submarine - and smashing it to a pancake, and that I'd be dead before even that happens.
And so, I argued that I would prove it to them. And so, I stole their submarine and now their military is after me. And so, I had to blow up the USS Tiny. And so, my some-number-of-minutes journey began.

The journey's beginning was no tough job. It was the usual start. First, bring the submarine down below the water and second, point it nose-down and keep it stable. Throttle up? Check. No damage? Check! Torpedoes? Bah, I don't need them! Wait... they're still in the tubes--!
Oh well, I'll just leave them in there. Let's get this submarine moving.

With that, grueling minutes passed. I slowly inched (okay, I didn't literally inch down there, I was going some 100 mph straight down at this point) my way into the increasingly void ocean, twitching at my controls to keep the submarine on a linear path. As each minute passed, I could feel my arm getting numb-- I mean, I could feel my submarine keep wanting to jerk in different directions. But I kept her steady.

Ack. As steady as I kept my submarine and as much as it occupied me, things started to get a bit duller. A bit darker. The islands now stood far above me and my patience waited together with me. "I gotta go deeper. 16,000 feet won't cut it!" I kept motivating myself. In the meantime, I paused to find out the deepest point in the Mariana Trench: some 36,500 feet... or was it 39,000 feet? Who knows. Whatever it was, I had to pass it.

20,000 feet, 25,000 feet... I'm getting closer. Behind me, everything began to vanish. The islands I saw minutes before were now just light streaks across the dark screen. In the distance, peculiar... yet recognizable... shapes and geometry came into view.

They were runways. Bridges. Whatever they were, they were there and I could see them.

This was it. I've gotten so close. 39,000 feet was just in my grasp and it was no doubt that I was going to surpass it. Regardless, with the passing of every thousand feet, even hundred feet, I felt the sense of victory - every inch of my thought planning this very script, this story I now write. With so much done by the community I sought to direct this towards, this was probably no new feat. But who cares? It's was awesome for me. I was going to get a bunch of parties, cake, and candy.

37,000 feet... I see no sign of the joys I was promised. All I see is a forever-fading atmosphere with blots of infrastructure strewn here and there. Above me, I saw an airfield. In the distance, I saw that same mess of geometry still prodding at my eyes, contrasting the black that surrounded it. Even the streaks of color of the islands always with me before began to fade from sight. The deeper I went, the more nothing I saw.

And here I stand, at 41,000 feet below sea level. There's nothing left in sight. Around me was a completely void, unfamiliar place. No harvest was present to reap and no prize stood to give me reason. It was just black. I level my submarine and look around. In the distance, a faint streak of light stood. Should I travel any further? Do I need to reach the point where I see nothing but darkness?

No.

My journey ends there.