Mythbusting is my favorite, yes. It is my attenuated, very watered-down version of the conspiracists who think the truth is always some secret that The Others (the Sheeple) aren't aware of. I do get the attraction, but I have also some sense that the urban legends arose for some milder reason, some prejudice common to the lot of mankind.
The archaeologist James Wright's blog about Medieval Mythbusting is a lot of fun. A sampling:
Spiral staircase in castles going clockwise to favor right-handed defenders backing up the stairs. Nope. It is not even mentioned until 1902 and the idea doesn't become popular until the 30s. It's on the lips of castle tour guides and in the brochures everywhere now, but it's new. Even with the new fascination in the 1800s with military analysis of castle design, no one mentions it. As with the myth of Ring-Around-Roses and the plague, ideas don't generally go unmentioned for centuries and then suddenly come to light.Theodore Andrea Cook, an art historian who is fascinated by spirals also keen on fencing and left-handers floats the theory at the turn of the century. By the 30s the popular historian Sidney Toy was asserting it as gospel. But spiral staircases aren't in the parts of the castle that tend to need defending, but in the remote chambers. Castles are designed to be impressive-looking, and many of the aspects reputedly for defense don't do that well.
Legends of secret tunnels beneath...well, just about everything, it seems. Tunnels from the manor to the local pub. Why? The manor had better access to liquor and women. Tunnels from monasteries to nunneries don't seem to actually materialise when one digs around. Any door that goes off an underground room in any direction is immediately concluded to conceal a long secret tunnel. But they don't. Break through the door and it goes one room farther. Monasteries and castles had many conduits ans sewers, always in the same order of the clean water from the river being directed into the kitchen and laundry first, under the privies last. Yet every town seems to have them, with tales delivered with chuckles that reveal the prejudices of the speakers more than the habits of the medievals. The hearsay with vague identifications may be part of the charm - "Oh yes, my grandfather said that he and another lad used to talk with the vicar about it years ago..."
Witch-marks, arrow marks, pentagrams. All have rather boring practical explanations. Though sometimes the real story is better than the legends. The shoes and stockings found embedded in constructions around chimneys and windows turn out to be there as a hopeful distraction for the evil spirits coming in through the drafts, diverted to a human-associated object and thus leaving the actual humans alone. The myth would get christianised by being reversed, that if you caught the spirit it would have to give you treasure in the stockings you'd hung above the fireplace. Rather like the leprechaun having to show you where the pot of gold is.
Ships timbers being repurposed as buildings. Only rarely. Forests were actually conserved and well managed until well into the Industrial Revolution, when the demand for charcoal became great enough to overcome the old customs. A violent storm in 1703 destroyed many ships off Norfolk, but the repurposed wood mostly went into outbuildings and fences. Wharves and barriers went into a few buildings in London when they were torn down, but ships, not so much. An interesting aspect of the mythology around it was Tolkien's focus on the destruction of trees and forests to feed the mills or the hellishness or Orthanc. He was brought up in and near Birmingham at the end of all the overwhelmed forest destruction, when the reforestation was still only partial and incomplete. It apparently made an impression.
There is a pattern to urban legends, which overlap with those of horror movies (that girl who loses her virginity? Yeah, she's going to die soon.) Those who don't "respect" the spirits have to pay the price. There are forever scandals to be covered up, always money, drink, and sex.
Wright supposedly has a book coming out about mythbusting eventually, but it isn't there yet.