The big challenge of this project was the historic and architectural importance of the stockholm public library, built in 1928 by Gunnar Asplund. This is the most visited place of the city by tourist and local users. Due to this, the idea was not interfere the existing buildings and minimize the visual impact that this could cause. We plan an imaginary pattern over the current buildings axes aligned to the near hill, and in some intersections we mark the boundaries of the new building, at the same time owed to the requirement of developing a buried project under the hill, we use this intersections points fot natural light to save energy. The form of the building emulates some parts of the hill where is located, but got some projections marking the position of the project. The prefabricated materials and the colors give a discrete presence of the building during fall and winter; on the other hand these characteristics make a contrast with the leafy vegetation of the area at spring and summer.