I wonder in what era the house was built .. along with the general area of location, like maybe in the Midwest of the U.S.? If old enough it is possible that an old cistern was altered into a place to hide runaway slaves, it could be a stop on the underground railroad. The man I was named after, a great, great grandfather ran an underground railroad stop from his business and it is now a historical site ... and it had tunnels and underground hidden rooms that were accessed through the basement and also came up in out-buildings like barns for multiple routes of entrance and escape. Then it might have just been altered to use for a cold room for keeping fruits and vegetables for a long time in the off season ... again depending on the era the house was built in.