Saturnalia is a survival horror game set in the fictional town of Gravoi, somewhere on the island of Sardinia, possibly modelled after the real town Gavoi. It is a small and cramped environment with nooks, turns, concentric stairways and cobbled alleyways. The game has a roguelike design with a large amount of customizability. During a session a cast of four characters is controlled, made available gradually. There is the geologist Anita, photojournalist Paul, drug addict Sergio , and Claudia, the daughter of the local bar's owner La Principessa. They all have their secrets and objectives with story fragments.
At the start of a new run the town's structure is randomized around certain key locations such as a church, a castle, a villa, a hardware store, a school, the mines, a dam, a town hall etc. Based on the chosen difficulty levels progress is either carried over or erased, mission markers and quests are enabled or hidden and there is optional permadeath. As the cast becomes available as the story progresses it is possible to swap between characters or ask them to follow. The game takes place at night with a permanent fog with hues of purple. There is also an unkillable creature that roams the town. Audio cues signal its presence. The characters need to outrun it as there is sprinting with limited stamina, cover their eyes or hide. It can also be distracted with sound or firecrackers. The game is not over when a member is captured and there are means of rescue with a brief window of opportunity.
A large part of the game is spent gathering clues and solving puzzles. These are stored on a separate screen where connections between characters, items and missions are shown. Prominent items are matches to light the environment or bonfires to mark a path, photos for Paul's camera, coins to buy items, energy drinks to restore stamina quickly and firecrackers to lure away the monster. The characters need to work together to locate items and certain actions or missions can only be completed by specific characters because of specific abilities, also leading to multiple endings. There are also phones used to call different characters in the town.
