The monastary of Carmen located in the basement of Catedral Inmaculada Concepcion is home to nuns who don't make any contact with the outside world. They do sell homemade jams, jellies, honey, wine, pastries, and trinkets, but without a shop or a display window. The product list is stated on the board. You simply ring the bell for an attendant. A nun will come to the wooden window but you cannot see her. Tell her your order & she will send it across the rotating screen. Similarly, send the money across & complete the transaction.
It feels like going to the confession booth at a church, with a nice prize at the end.