A plethora of archaeological finds show that the underground space was a place of vital importance for people. Caves became the home of many prehistoric small or large clans and families, as they provided them with safety from the weather, animals and external dangers. Over the years, many civilizations have found "shelter" in the underground space, in a more organized way, for their survival and development.

Nowadays, architect-researchers have to deal with the constant need of city expansions and their various problems, such as extreme weather conditions, which lead them to the search of new environmentally friendly design and construction solutions. The use of underground space is a new way to solve many of the above issues.

The present research work will deal with the reasons for the utilization of the subsoil, the benefits provided by this space, regardless of the use of the construction and an attempt will be made to answer the question why architecture is now turning underground.

Therefore, the project, firstly, analyzes the basic concepts of space, above or under the ground, and attempts a throwback to the connection between man and earth. Secondly, historic examples of the underground architecture worldwide will be given, examples that still standing out due to the intervention in the subsoil. Finally, yet importantly, conclusions will be drawn for the reasons that led people underground and the benefits that underground space provides.

Besides that, examples will be given from contemporary underground constructions, of various uses (residence, storage, sports facilities etc.). The project attempts to find the reasons why architects nowadays turn underground and the benefits of the subsoil.

Caves protected the humanity millions of years ago, underground space gave a home to ancient civilizations. Today, underground space gives again, through its use, a chance of improvement for human life.