The main building of the National Museum in Prague was built in the end of the 19th century. There have not been any significant repairs made since the opening of the building. The historical building is in poor condition and therefore the reconstruction is necessary. In pursuance of the huge reconstruction, the deepening of one of two atriums is planned. New ground floors for exhibitions halls will be constructed. This place will be connected to another museum building by a connection tunnel. This paper presents geotechnical works during the reconstruction of the historical building of National museum. The construction site is located in the area of complex geology with variable depth of the bedrock. The bracing and underpinning is designed with the help of the combination of several special foundation engineering methods e.g. jet grouting, micropiles, soil nailing. Great emphasis was placed on minimization of bracing deformation to prevent any damage of the existing historical building.