Castle well

It was often the most costly and time-consuming element in the building of a castle, and its construction time could span decades.

In medieval times, external wells were often poisoned, usually with a decomposing body, in order to force a garrison to surrender.

Over the projecting "chimney" so formed, a fireplace was built that sucked air through the well shaft below.

Fresh air (and hence oxygen) circulated through the artificially built U-shaped pipe so created, its two halves being separated by the dividing wall.

The well located in Zbiroh castle (now château) in the Czech Republic is 163 metres deep.