The developer of Full Fathom describes it as a “thalassophobia sim”. You are the lone engineer on a rustbucket submarine exploring the dangerous waters of a submerged country in an alternate reality 1990s. The warning lights on the control panel are flashing, a buzzer is spluttering like a dying bluebottle, and your robotic assistant is about as useful as an umbrella in the Mariana Trench. Things could not get any worse. And then you see it. Something in the green haze outside. Something with a tail.

We’ve seen Full Fathom breach the surface a few times in various Screenshot Saturdays but now there’s a playable demo as part of Steam Next Fest. In the most pitchy of elevators it is “horror Subnautica”. You can leave your submarine to swim through the ruins of flooded skyscrapers and houses, salvaging for fuel tanks and canned food among other necessities. But you also need to pilot the submersible (albeit in quite an auto-piloty way) between numbered points of interest in the ocean.

So yes, it is a bit like the wet wandering of Unknown Worlds’ survival game. Yet there is something greebly and clunky about the machinery of Full Fathom. This is not the smooth and sleek Frutiger Aero interface of Alterra Corporation, but a grimy, barely functional platter of non-descript buttons and unlabelled levers. Switches and handles and valves and cranks, all of which must be figured out mostly by, well, pressing them. Like this!

Oh dear. All the lights just went out.

The game’s demo went up in July, so I’m a little late to the underwater party. But I won’t let that stop me. “Use your throttle,” advises a handy leaflet in the control room. “Holes are bad.” In the end, I barely get the submarine moving and almost perish in a nearby ruin. Outside the ship, spikey urchins will puncture your suit and sap your strength. I get lost in a dark house when my flare goes out. Luckily I am scroungy enough to have picked up a can of compressed air for emergencies.

I can’t fully blame myself for the incompetence. This is your warning that the demo is quite hands-off when it comes to tutorials. There is some guidance in the form of pop-up hints but mostly you are left to figure out the details of all these buttons and cranks yourself. Your robotic anchormate will give intentionally useless advice and feels there to deliberately unnerve and enrage you with his Clippy-like face and passive-aggressive remarks. I enjoy hating him.

Meanwhile, there is a frame story that sits outside all of this, full of fun meta touches. The pause menu here is a set of controls mounted on the wall. A neon hotel sign reads “Alpha Demo”. An authentic looking exit label on the door reads: “This door will exit the game”. When you take a screenshot with Steam’s built-in screenshot key, F12, a camera flash goes off in-game. When leaving the pause menu for a long enough time, it will become a Windows style screensaver circa 1998. I think that’s cool.

It’s tough to stand out among the 1700+ other demos in Steam Next Fest, but if you are channelling the deep dread of Subnautica, the chunky UI of Nauticrawl, the panic of Barotrauma, and the rust of Iron Lung, you will immediately have my eyes. It is deeply reassuring to me that, even after all these decades, game designers still know how to make pushing an unmarked button equal parts hilarious and terrifying.

For anyone who needs more recommendations of games of this type, but likes sci-fi more than sub-fi: try the delightful tactility of Objects In Space or, more recently, the confused claustrophobia of Tin Can.