The first province on the Camino de Santiago. To be honest I started in France and crossed the french Pyrenees but everything else after that was pure Navarre.
Undoubtedly the hardest section of the Camino Frances as your body hasn't gotten used to walking this much.
Wikipedia: Navarra (Navarre) is a geographically diverse region in northern Spain. A medieval Basque kingdom, it was annexed by Castile in the 16th century. Dotted with remote villages, its capital and largest city is Pamplona, famous for its annual running of the bulls. Pamplona has 16th-century fortifications, the Gothic Santa María la Real Cathedral and the Museo de Navarra, with archaeological and art collections.