I've encountered a couple of these in my travels:
The Haggis - said to be a four-legged creature that races around Scottish hills so speedily because its right hand legs are shorter than the legs on the left hand side. Of course, haggis that travel *anti-clockwise* round the hills (and thus have the left hand legs shorter) are much rarer.
And visiting Australia on a bookship with 350 (mostly young) people from 40 odd countries, we were invited to sign up for an outing - as we often were in different ports - for a bunyip hunt. Fortunately I knew better but some friends blithely signed up and then did their best to obliterate their names when they realized they were being had! It wasn't the tidiest sign-up sheet outside the dining room. Wikipedia tells me however, that the bunyip wasn't quite the figment of the imagination of Aussie practical jokers I initially thought:
https://en.wikipedia.org/wiki/Bunyip
I also have the vaguest recollection of my Dad, who served 30 years in the Royal Navy, telling me that there was a similar practical joke played on the new crew in Malta. They could sign up for a 'malta dog run' (either a run ashore (recreation) or maybe it was for a fitness thing, I can't remember. IIRC the fun was that 'malta dog' was a euphemism for diarrhea. One for the Imperial Navy recruits I think.
A nessie equivalent of course could go either way. Yes, everyone *thinks* it's just tourist fodder but the poor PCs are either on hand or have a patron getting them into the right place at the right time to discover that it's not as mythical as was thought - and it is *not* happy about the disturbances a recent upswing in the numbers of tourists/journalists/crackpots have caused.
Then there is, of course, the Reginan rakon which is an otherwise ordinary looking mammalian omnivore a little larger than a cat. However, visitors to more rural areas maybe warned to check both inside and under an open topped air/raft as they like to nest in warm spots. Hire companies are said to deduct the entire deposit from any air/raft that has rakon fur left on the upholstery or the vents as it is *so* difficult to clean off. In actual fact rakons will almost always flee from any sign of human/sophont activity and even if they weren't so shy, their fur is unlikely to moult.
Slightly related:
I did a short stint in a factory once and was hazed by being sent for glass nails and a long weight - so perhaps new crew are sent for a Jump recycler, a 'Fresher mint (probably needs some lead up to that one) or a sonic screwdriver. ;-)
tc