Core Keeper begins with the main character going on an expedition, during which a mysterious artifact is found that creates a voluminous portal that drags a person into an unknown place. Waking up in an ancient cave, the adventurer encounters a variety of creatures, rare resources and valuables. However, danger awaits at every step, capable of instantly killing a lonely wanderer.

The project has a single-user mode and co-op for up to 8 participants at the same time. The larger the group, the more difficult the passage becomes, increasing the number of opponents in the locations, but also the number of items falling from treasuries and the environment. The player will have to stay alive while traveling through the mysterious underground world. Tools are needed to extract resources, which are required for construction, crafting, and survival.

The game area is endless and procedurally generated. The most valuable resource is hidden crystals, which are used to create the best items. The gamer can develop technology, gaining access to more advanced mechanisms that generate energy and convert ordinary materials into valuable items. The construction system allows you to build arbitrary rooms, houses and rotate objects or change their sizes. The hero needs food, obtained as he explores the cave or by growing seeds.