If you’re familiar with Sunless Sea, you’ve doubtless been painfully acquainted with the Victorian-tinged horrors of death on its open waters. But there’s something infinitely worse about the dark — and plunging into the depths of the Zee is exactly what awaits players willing to brave Sea’s newly released diving expansion, the appropriately titled Zubmariner. For Failbetter Games, ratcheting up the fear in expanding their world was of course always the point. And with fans already scarred from the terrors that lurk beyond Fallen London, the most logical conclusion was probably also the most likely evolution: a fear of the unknown.

“It’s much darker at the bottom of the sea, and that gave us the opportunity to leave a little more up to the player’s imagination,” says Sunless Sea’s director, Liam Welton via email. “You can suggest something terrible scuttling in the darkness with lighting and some horrible sound effects, then let fear do the rest. It’s good that we had the darkness to use as a blank canvas for the imagination.”

By way of a Jules Verne-esque invention, explorers in Zubmariner can turn any vessel into — what else? — a zubmarine, offering an entirely new, and more frightening, world to traverse. (“People can populate it with their own nightmares,” Welton says.) For the expansion, Failbetter has pushed a philosophy of what they call “trespass,” the notion that you’re a visitor in a hostile place. Quite simply, you don’t belong there, and whereas Sea only hinted at the dread beneath the waves, here you can discover it up close and personal.

“When considering [*Zubmariner*'s] environment, it became clear how hostile it would be,” Welton says. “Airless and lightless, you would be stumbling around trying to make sense of the location. It would be a place that would resist your presence. It made sense to embrace that and make it a place where not only the environment, but the places and the people themselves, made the player feel unwelcome.”

Zubmariner adds additional stress on players by making them monitor their air supply; not only are you pushing into an abyss of darkness — a place where you might discover that a distant light is a massive otherworldly beastie, or simply see a city-sized shadow pass over your zubmarine — but you are doing so knowing that running out of oxygen often means a grisly end.

“We wanted to give the player access to a location where there was always an interesting choice to be made, if you were willing to take the risk,” Welton says.

But when you set the bar for psychological trauma at cannibalism (and worse), is a fear of what you may find in the deep really enough to fill you with unease? Maybe not, but it wouldn’t be the world Sunless Sea without equally unsettling storytelling. Here, the team is taking reference from all manner of literary influences, including (as I’ve learned) some British folklore dealing with fairies.

Not that you shouldn’t be alarmed. Narrative director Chris Gardiner recently brought up a particularly great example from Zubmariner about a society of drowned sailors during a panel at EGX; they live in Dahut, essentially a facade of a world, but accept it at face value, a choice which players themselves are given. Whether you want to live in the lie or face the reality beneath is, of course, up to you.

“[One] inspiration is the Ballad of Tam Lin, where a mortal wanders into a fairy domain, enjoys its illusory delights, and then is confronted with the (often horrifying) truth behind them,” Gardiner says.

It also wouldn’t be Sunless Sea without the strength and sophistication of narrative.

“My favorite thing about [writer] Emily Short’s approach to Dahut is how delicately it handles the division between truth and deceit,” Gardiner say. “There’s a moment when you catch a glimpse behind the illusion, and she describes the grasses stirring, and you see crabs scuttling through them. A lesser writer might have had everything go all wobbly and the illusion just disappear and be replaced by the truth — Emily suggests the truth is always there, and you could see it if you just looked at things from a different angle.”

That Gardiner can speak so eloquently — and enticingly — about something assuredly so nightmarish is proof of itself Zubmariner is worth the journey. And perhaps even the fear.

Steve Haske is a Seattle-based writer and sometimes a creator of stupid art. His work can be found on VICE and Playboy. Iain Glen is his Virgil.