This rather nice external staircase is typical on vernacular buildings in the Loire Valley, south-west France and probably many other regions in the country. The one in the photo can be easily seen from the path up to the Source Saint-Marc in Chaumussay.
Staircases like this first appear in the 15th century, providing access to the interior of the house, which sits on two floors, plus attic, above its semi-underground cellars. Staircases themselves don't get to be integrated into the body of the house until the 16th century, and even then they were open to the elements very often. Since they acted as chimneys drawing warmth upwards they were problematic in an age when heating was difficult. If you wanted to access a different floor of the house it was normal to step outside onto the staircase, go up or down, then back in. The staircase itself was sealed off from the interior of the house to retain warmth inside and to ensure the staircase took advantage of natural light. In higher status buildings staircases were often enclosed in their own tower, attached as an annex to the main building. But even the grandest houses such as the chateau of Azay le Rideau had staircases which were originally open front and back, and it was not until the 17th century that fully enclosed internal staircases became the norm for grand houses. The open external staircase persisted for rural vernacular buildings well into the 19th century in many cases though.