This paper presents an interdisciplinary method designed to study urban ambiances. The main goal of the commented city walks approach is to gain access to the in situ sensory experience of passers-by. The key is to acquire accounts of perception in motion. For this, walking, perceiving and describing are simultaneously required. Commented walks are based on three central hypotheses: the situationally-rooted nature of perception, mobility as a condition for the existence of perception, the interlacing of words and perception. This method is applied here to the Grand Louvre in Paris.