Geothermal energy recovery has become more and more popular during the last decade of high oil prices, and it has been supported by intense research activities. Geothermal energy is characterized as an inexhaustible and continuous source, requires only a small footprint facility and is completely CO2- and waste-free. The global demand for energy is also believed to increase dramatically in the next few decades, which makes it necessary to introduce further energy supplies to the market, and that, too, in a cost competitive way. However, geothermal energy systems are more expensive in terms of investment costs per power output gained. Most of the costs are associated with the construction of the wellbore. To make geothermal systems financially more attractive for a broad use in the future and to give an incentive to operators and investors, the total costs must be reduced. The general idea of this thesis is to utilize existing subsurface facilities, like mines and tunnels, and construct a geothermal recovery system within them. Owing to the existing overburden of the rock, the starting point for the geothermal well is already at an elevated temperature level. The same superior thermal level can, therefore, be reached with a shallower well, compared to an ordinary wellbore drilled from the surface. The amount of overburdening equals the meters of wellbore saved and, hence, leads to lower associated drilling costs. A general overview of the available geothermal systems is given here, and – based on a project region – the preferable system is chosen. The project region in Styria, Austria, is introduced, and its environment discussed. The existing project mine is evaluated towards feasibility to transport and rig-up a certain drilling rig inside a tailor-made cavern. Suitable drilling rigs for the scope of this project are evaluated, and related HSE aspects are considered. Furthermore, it is critical to understand the factors that contribute towards cost, their magnitude, and how they influence the economics of the project. Several casing design scenarios are presented and their costs calculated. Finally, the technical and economic viability is discussed, and the advantages of a geothermal probe located at a subsurface level and potential pitfalls summarized. In addition, recommendations for further projects are given.