Look up "Iron + Maiden + torture" (to exclude references to the musical group), and you'll find links to the "medieval torture device." The idea of a tax with spikes in which you'd put a human and then close the doors sounds "medieval" to most. The problem with that adjective is that there is no evidence that the Middle Ages used them. The earliest references don't appear until the 16th century.
On August 14, 1515, a German who had forged coins was tortured with a device called the Iron Maiden. It was a cabinet sized for a human, lined with spikes. As the doors were slowly shut, spikes penetrated the forger's body just enough to cause excruciating anguish but not enough to kill him. Crying in vain, the forger—according to the tale—lived two days.
In fact, there was a much earlier reference that might have inspired it, from no unlikely a source as Augustine of Hippo's City of God. In it, he describes a martyr whom the Carthaginians shut "into a tight wooden box, where he was forced to stand, spiked with the sharpest nails on all sides so that he could not lean in any direction without being pierced."
Such a device would not have been casually made or kept. You would expect it to be maintained by whichever lord had it made. We have plenty of remnants of torture devices, but the first iron maidens that exist today were not constructed until (drumroll) the 19th century! The first one appeared in Nuremberg (see illustration) no earlier than 1802. Several have been made since then, mostly as tourist attractions in castles and museums.
Most modern historians agree that the "Iron Maiden" as it is thought of was not only not medieval, but not a torture device used in any era.
While we're on the subject, tomorrow we'll look at some other medieval misconceptions. See you then.