Narrative:

You play an explorer accompanying a research team to Lake Baikal in southern Serbia.

The team has been heavily funded by a corporation to explore the depths of the lake, to investigate past claims of strange activity. Word has it, that artifacts wash shore during the summer, leading experts to believe that an ancient city lays dead at the lake's depths. And the corporation in question wants to uncover and document it during winter rather than the much more hospitable summer months so that it beats its competitors to the punch.

Your character is equipped with cutting edge diving gear and happens upon a tunnel of ice leading to a cavern where the water breaks. Unfortunately for your character, part of the team misuses their new fancy tech to displace large blocks of ice from the path of the boat and accidentally creates a ripple effect that traps you character in the cavern, though still able to communicate with the team, barely.

Another member hypothesizes that your character will be able to find a way out based on a scan they did of the caverns. It appears this place used to be above the lake, due to some telling signs like dead trees. And it was home to an ancient city, their belongings strewn about all over the place, including what appears to be the incredibly illusive Greek Fire, along with other lost relics.

Soon though, things don't seem as simple. Large voids in the scan account for giant unreal structures, far beyond what the ancient city seemed to have stood for. Strange noises recorded account for the beasts who call this place home.

Your character must find a way to the surface, least he/she is trapped Beneath the Ice like the ancient city they've found.

(image from http://siberiantimes.com/other/others/features/f00... )

Gameplay:

Your character makes use of the tools left behind by the people before to overcome the challenges ahead. As the history of the ancient city the character has uncovered, so to does his/her own story.

The player will be killing enemies with the combat and defensive tools found. He/she may even set up traps. Resources, however, are as limited as the enemies, and the player will have a fairly difficult time fighting late game enemies with simply melee if he/she doesn't manage equipment properly. But that's the nature of the game, it won't be crushingly unfair though.

The game progression will be designed so that further up the cavern you character travels, the harder enemies, but more advanced the equipment to handle them become. This is accompanied by the narrative in a well rounded way that makes it seem less game-y in execution.