There may well have been two or more Castles of Maidens, and it or they are not quite like the "Castle Anthrax" which Galahad finds so full of choice damsels in the film Monty Python and the Holy Grail.

Perhaps the most notable account in Malory of a Castle of Maidens is; seven years before the Grail Quest, Duke Lianour had held this castle. Seven wicked brothers moved in, raped his elder daughter, and murdered him and his son. When the daughter predicted the brothers would all be defeated by one knight, they decided to hold prisoner all knights and ladies who passed by.

[A]nd therefore is it called the Maidens' Castle, for they have devoured many maidens.

[A "maiden", in older and broader usage, can be a virgin of either sex.] Galahad arrived and defeated all seven brothers in battle, but did not kill them. Fleeing, they ran by chance into Gawaine, Gareth, and Ywaine, who did kill them. The elder sister was dead by now, but the Duke's younger daughter was made mistress of the castle and lands.

The spiritual significance [hardly anything happens during the Adventures of the Grail which is not a parable] is that the prisoners represent the good souls that were in prison [Hell or Limbo] before the time of Christ, and the seven brothers represent the seven deadly sins. This Castle of Maidens was "a strong castle with deep ditches, and there ran beside it a fair river that hight Severn". It might be near the source of the Severn, at Llanidloes, Montgomeryshire, Wales.

Malory also mentions a Castle of Maidens as the site of an important tournament between the King of North Wales and King Carados of Scotland. This tournament is remembered in X, 58:

Sir, said Palomides [to Tristram, as they approached Castle Lonazep and saw the tournament set up there], meseemeth that there was as great an ordinance at the Castle of Maidens upon the rock, where ye won the prize.

This may be the same castle as that of XIII, 15-16; the tournament could have been held before the seven wicked brothers moved in. By the account of the old religious man who explained its history to Galahad, though, there would have been no reason to call it the Castle of Maidens before the time of the seven brothers.

Glennie identifies the Castle of Maidens with Edinburgh, speculating that the name may come from a house of nuns. This contradicts both Malory's placement of the stronghold on the Severn and his tale of the seven brothers.

If, however, the Castle of Maidens of the tournament is considered to be a different fortress than Duke Lianour's, then Edinburgh could accomodate it nicely, especially with Malory naming Carados of Scotland as one of the tournament's promoters and Glennie mentioning the "fortified rock" of Edinburgh.

John W. Donaldson briefly identifies the Castle of Maidens as "near Dorchester", for no reason that I can see.