Today there is a second floor or attic in almost every country house. Naturally, there is a staircase. Depending on its width, the space under the stairs is used for different purposes.
In large capital houses, this place is usually included in the construction plan and equip some kind of capital room under the stairs, starting from the library and ending with a small kitchen.
In a small summer cottage, so that the underbrush space does not turn into a landfill, you can make small shelves there, as in the photo, where there is a lot of space for a wide variety of things.