Use of underground spaces is positive in relation to visual intrusion. The underground spaces are perfectly integrated in the environment. For linear projects, for example, they allow to eliminate embankments which produce a very negative visual impact. This is especially interesting in landscapes of high value, such as mountainous areas, but also in urban areas.
The construction of a tunnel in a city can be considered as a non-alteration of the "cityscape"; it can also be an opportunity to create green spaces to rise the environmental features.
The project to build a tunnel on the Seattle water front instead of the existing viaduct will completely modify the aestetics.