In the days before electricity and refrigeration, keeping food for a long time was difficult. If you wanted milk in the summer, it had to be kept cool until you drank it. If you wanted to keep potatoes and apples for many weeks, you had to find a way to keep them cool without freezing them. Creative farmers long ago realized that the underground temperature was cooler than the air temperature in summer and warmer than the air in winter. They created root cellars like this one, which is still on what was Broad View Farm (aka Nevius/Van Zandt farm), to store vegetables, fruits, nuts, and other foods.
According to Bill Van Zandt, who grew up west of the where the root cellar is located, there was an apple orchard of about 30 trees about 150 feet to the east. The apples were stored in the root cellar for use or resale.
Notice that the building is made of stone for insulation. As you enter, you would step down to the underground storage area. Farmers would fill the root cellars at harvest time and use the yield from their farms for many months. It's hard to imagine this way of keeping produce fresh in an era where food is available from all over the world all year long.
UPDATE
After reading this post, former Blawenburg resident Richard Van Zandt contacted his father, John Van Zandt, to ask about the root cellar. He confirmed that it was used for apple and vegetable storage in the last century. He also shared this recollection:
"In addition Dad thinks that even long before he was born it was used to hang meat—also for cool storage—and may have been a smoke house or “meat curing” house even before that. I remember large metal hooks built right into the ceiling. Hooks were spooky and we used to say that they hung naughty children on them as punishment."
As you can see, there's a lot of history in Blawenburg, even in one mundane root cellar.