20k Leagues Under the Sea: HSS

[The elevator deposits you in the interior of a spacious submersible with a decidedly steampunk aesthetic. All of the metal is brushed bronze, and the navigation tools look to be turn of the century]
[Through the periscope, you can still see the sky; the water visible through the circular windows is a pale blue-green, kissed by filtering sunlight]

RULES
Welcome to 20,000 Leagues Under the Sea!
Your goal is for your team to travel a distance of 20,000 leagues in your submersible. The teams that continue the longest will win a ~fabulous prize~: instant and painless revives, and full healing for one team of their choosing.
The journey won't be easy, though. Every time you choose to take your submersible further into the briny deep, you run the risk of suffering a fatal setback imposed by the challenges of the sea.
You can turn back at any time, safely surfacing. However, fortune favors the bold, and once you ascend, you cannot return to the challenge.
So the decision each round is up to you: will you boldly press onward, to discover the unknown? Or will you return to the realm above, and leave behind the ocean's watery secrets?