35MM is the story about two male travelers in a post-apocalyptic environment in Russia. The game starts in medias res when they are already on the road. The player controls only one character: Petrovich. Their history is then revealed gradually by progressing through the game, through their conversations, documents and events. The game consists of several sequences with a blend of different genres. The majority of the game is spent exploring desolate environments, either abandoned or with traces of the dead or looters. The entire game has a somber look with washed out colours. There are also some NPCs, but most of the game the two spent their time alone.
Each sequence usually has a large environment that can be explored freely. When wandering too far however, invisible barriers are used. There are villages and cities, the countryside with fields and forests, a flashback in a hospital, an underground complex and so on. The other traveler walks by itself and does not necessarily need to be followed. Most sequences have a main objective to be completed, but the player is encouraged to explore the entire environment to get most of the game. This is usually rewarded with items, documents and often gruesome discoveries or interactions that are not pertinent to further the game. Some of these encounters trigger a flash for the main character, revealing something about his past.
These parts take up most of the game and resemble adventure titles as there are often environment based puzzles with objects that need to be found through exploration. Some puzzles are complex, requiring careful observation of the environment, deduction or using certain machinery. At the same time there is a small survival element to the game, collecting first aid kits, batteries for a flashlight, food, ammo, lighters and matches, gasoline and so on. Hunger and health are however not a constant treat. While there is a lot of tension, usually through the ambiance and the environment, there is no real horror to the game, and no zombies, fantasy or supernatural elements. Next to gathering loot there are many optional photographs, codes for safes and easter eggs that can be discovered. Certain objects can be manipulated or picked up to be used elsewhere. Basic tools include a knife to cut rope, an axe to hack through doors and so on. Some tools or items are present, but only used a few times, such as a tire iron or a lockpick tool.
There are also a few action elements, such as chases, quick time events and full action sequences with a regular pistol and a machinegun. Guns have a small amount of ammo and the player needs to search thoroughly to find more. It is however not needed to constantly run around with a gun for quick threats, most of the game is based on suspense and the action sequences are confined. The character carries an analog camera that can be used to take photographs at any time.