Der Bau (1923-1924) is a fragmented narration by Franz Kafka, published after his death and against his last will. It is characterized by precise and figure-centered descriptions. The reader begins to immerge in the environment of an unknown figure living underground. Within the first paragraph a situation opens up, where this figure identifies itself as an architect, constructor or experimenter. Its language evokes spatial ideas, ideas of architecture as living space, physical and body space, space of specific knowledge and visions. The narrators descriptions contribute to the generation of a spatial impression. This project takes the narration Der Bau as a starting point for reconstructing its literary spaces. It is based on the idea, that fictional and unbuilt spaces are part of our cultural heritage. The focus lies on speculative architectural work, a poetization of architectural procedures and digital techniques. With the aim of developing spatial models and procedures, that understand architecture as the construction of possibilities.The story of Der Bau is told from the perspective of a figure, who has devoted its life to the construction of a subterranean topography. The resident is builder and observer at the same time. In spatial terms Der Bau is outlined as a system of tunnels and rounded excavated spaces, which serve as living spaces or storage compartments but nonetheless as a protective bunker.Any changes to the underground structure directly reflect the inhabitants mental condition.After a few years of designing and constructing, the residents reflects on the configuration of its spaces, their function and their texture but also about their protective character.Literary studies on the narration assume a threefold partition of the text: In the first part the figure is moving through its building and describes it. In the second part it observes, measures and tests construction principles. In the last part a noise of a potential enemy emerges. The inhabitant tells about fears of an attack and plans changes of certain parts of the building. It ends in an imagined collapse of the burrow, which seems to be the only possibility to protect the burrow from intruders. This project adopts this partition and its principles:The first part, reports on the construction of a burrow, is on reconstructing several described spatial scenes. The second part, on material and operation logic, is an exploration of subterranean spaces, as well as on a controlled apparatus which is digging through sandstone. The third part, a possible reconstruction of the burrow / entering Der Bau, builds up on the investigation from the previous parts and deals with the attempt to reconstruct the underground construction Der Bau.