This 1km-long stretch of the Grottes de Médous - a cave network discovered in 1948 - contains numerous concretions, including stalactites and stalagmites, as well as broad swathes of calcite in shapes reminiscent of cascades, huge organs and draperies. The tour ends with a 250m boat ride on an underground river formed by water from the Adour, which comes back out into the open in the grounds of the Château de Médous. Sadly the state of the caves is gradually deteriorating due to the large number of visitors.