Intensive research over the past decades has greatly improved our understanding of processes operating in the deep ocean. There has been a particular focus on continental margins, as sediments deposited in these areas can provide a high-resolution record of past climatic changes, as well as serve to host some of the world's major hydrocarbon reservoirs. However, the exploration and understanding of the deep ocean remains one of the great challenges of the 21st century, and many fascinating features still wait to be found. The potential for new deep-water discoveries was recently highlighted during Meteor cruise M58/1 (depart Dakar, Senegal, 21 April 2003, return Las Palmas, Spain, 12 May 2003) of the Research Center Ocean Margins at the Universit¿t Bremen in Germany. A spectacular 400-km-long submarine meandering channel system was discovered off Mauritania. In this article, the system is called the Cap Timiris Canyon (Figure 1). Although a series of incisional gullies at the shelf break and uppermost slope have been described before, the enormous size and complex morphology of this submarine channel system were previously unknown.