Garderobes were medieval toilets in large public buildings and castles. They were often holes in the outer walls of these buildings which dropped into cess pits or moats (depending on the structure of the building involved.) Many can still be seen (from the inside and out) in Norman and Tudor castles. They became obsolete with the (re)introduction of proper plumbing.
They also served as useful places to store clothes, as the pungent smells deterred moths. This is the origin of the modern word wardrobe.
Most of Wikipedia's text and many of its images are licensed under the
Creative Commons Attribution-ShareAlike 3.0 Unported License (CC BY-SA)