Amnesia: The Dark Descent is a survival horror video game released in 2010 for personal computers such as Linux, Windows, and Mac OS. The story revolves around the protagonist, Daniel, who is trapped in a large, abandoned mansion and faces the danger of monsters and tries to solve complex puzzles. Amnesia: The Dark Descent is a first-person adventure game with survival horror elements. The player controls Daniel, who must navigate the castle of Birnenburg while avoiding various hazards and solving puzzles. The gameplay retains the physical object interaction used in the Penumbra series, allowing for physics-based puzzles and interactions such as opening doors and fixing machines. Smaller items can be stored in the inventory, while larger objects can be lifted by holding down the mouse button and pressing or dragging the mouse. Objects such as doors or levers can be manipulated with the mouse in a way that simulates the movement of said object. The difficulty level of the game can be adjusted before starting, but cannot be adjusted once the game has started. In addition to the health bar, Sanity must be managed, which centers around a "fear of the dark" mechanic. According to designer Thomas Gripp, "the idea was basically that darkness itself should be an enemy." Sanity is reduced by staying in the dark for too long, witnessing disturbing events, or looking directly at monsters. Low Sanity causes visual and auditory hallucinations and an increased chance of attracting monsters, while completely depleting it results in a temporary reduction in movement, or death on higher difficulties. Light sources help restore Sanity, and if none are available, Daniel may use small canisters to light candles and torches or deploy an oil-burning lantern. However, both the number of canisters and the amount of oil available are limited, even on higher difficulties. If a monster sees Daniel, it will pursue him until he escapes its sight. Daniel has no way to fight off monsters, so he must either avoid being seen or run away. Daniel can only withstand a few attacks from a monster before dying, which will load the last save of the game. The player can restore Daniel's health using laudanum, which is found throughout the game. The player can hinder monsters by closing doors and building barriers from nearby objects. However, monsters can destroy doors and knock over objects. Hiding in dark areas where monsters won't notice Daniel is also effective, but will reduce Daniel's safety. On higher difficulties, monsters will move faster, deal more damage, and search for Daniel for longer periods of time. Amnesia: The Dark Descent received very positive reviews from critics, with continued praise for its ominous atmosphere and horror elements: "By placing a heavy emphasis on sight and hearing, the distance between the player and the game is radically reduced. This is enhanced technically by John Walker's use of stone, paper, and shotgun." He went so far as to say, "I think it's safe to say that Amnesia is the most successful scary game ever made." He also added Amnesia to his top ten PC games, saying, "There are a lot of so-called 'horror' games out there, this one is no joke. "You'll be rocking back and forth and crying in no time." Friction Games showed some trepidation at the game's initial sales after the first week, but were encouraged by continued sales throughout the first month after the game's release; by early January 2011, the developer reported that nearly 200,000 copies had been sold, stating in response that "with these numbers in hand, we must admit that it gives us new confidence in the PC." The game continued to sell and in July 2011, it had sold nearly 350,000 units. At the 2011 Independent Games Festival, Memory of Amnesia won awards for "Excellence in Audio" and "Technical Excellence" along with the "Direct2Drive Vision Award" which included a $10,000 prize. A year after the original release of Amnesia, the developers revealed that they had sold approximately 391,102 units and continued to sell approximately 6,000 units per month. They also released details on how much money each platform makes for them by analyzing sales from their online store, with the figure coming in at $10,000. 70% of sales came from Windows users, 15% from Linux users, and another 15% from Mac OS X users. However, Friction noted that their store was the only place anyone could buy the Linux version of the game, while the Mac OS and Microsoft Windows versions could be purchased from other sources, meaning that the overall percentage of Linux sales was actually smaller compared to the other platforms taken collectively. Noting that their Mac OS X sales did not decline from their own store even with services like Steam picking up the game for that platform, meaning that it was not stealing customers from their store but instead opening up a new market, they decided that this would provide a good incentive for other stores to support Linux as well. As of September 2012, the game had reached an estimated 1.4 million sales. In 2011, Amnesia was ranked as the 34th best adventure game ever released. In 2015, Kotaku ranked it as the second best horror game of all time, beaten only by . T, but it moved to number one after PT was removed by Konami. In 2017, GamesRadar ranked Amnesia as the third-best horror game of all time, although in a revised list for 2018, the game moved to number 13. In 2018, The A.V. ranked it the seventh-greatest horror game of all time in a list of 35 games.