On 27 November 2003 at approximately 12 pm a failure occurred without warning on a 52° mudstone slope adjacent to the customer carpark of a large department store in Avilés, Spain. No physical damage was caused to the department store but a high-pressure water main in the upper part of the slope was ruptured. A major concern was the proximity of a six-storey residential building at a distance of only 10 m from the crown failure scarp. Additionally, the resulting spoil caused the closure of the goods access road and rendered unusable numerous parking spaces. The estimated volume of the failure was c. 2000 m3. Following the failure, emergency remedial works were implemented to ensure the short-term stability of the failed mass and prevent possible retrogression of the failure towards the buildings. Geotechnical instrumentation was installed to monitor the stability of the area. A back-analysis of the failure was undertaken and, in conjunction with the results of the site characterization, led to a definitive solution: a rock-fill gravity retaining wall and an upper anchored rock-fill gravity retaining wall were designed and constructed, and the water main was re-routed away from the slope.