Don't know the actual intended use of this particular outbuilding here in Illinois but back home in Penna, they were built over underground springs. The foundations were dug out so that water would flow through a cement floor basin and used to cool the fresh milk as well as other items. Sort of like a cold cellar but colder. The general term was Springhouse and so that's what I still call them whether they are or not. Could just as easily be an equipment shed or a tack room. ps; I obviously not talking about the silo in the center.