It is a long time since I offered you a quiz. The following free standing structure is unusual, this stone feature is normally to be found built into a wall - I have one in my own garden. Alas it is not historic, ours was built into our drystone wall at my request. They should be south facing, and many can still be found right across Britain today, some dating back as far as the 12th century. They can still be seen in the fortified walls of medieval towns, castles, monasteries and in the walled gardens of many stately homes or large properties.
a) What is the official term used for these structures and b) The special name given for the items that they contained?