The Yellow Rocket is a one-seater

You climb into the yellow rocket all by yourself and instruct the crew to lower you into the drink. The water line passes over the front view port like a thin film transporting you to a whole different world that you've visited time and time again. You hear the clamps retract and your free to move anywhere. Down being the primary direction.

Several minutes pass with nothing more than the odd fish or jellyfish floating by. The endless blue void was being as entertaining as it's always been when you were sinking. After almost an hour of sinking, you see some sand fade into view in the Yellow Rocket's headlights. You slow decent and start exploring.

You slowly start searching for any clues that might lead you to the lost city. You have to travel slow or else the sub's propulsion will disturb the soil and kick up a cloud of dust. Down here, the ocean current barely moves. Sand clouds will obscure vision for several minutes or even hours.

In your search of the immediate area, you manage to find a cave that's just big enough for the Yellow Rocket, a trench with rock walls towering high, and an unknown wooden ship that seems to have been resting here for more than one hundred years.