Flick through a Guinness book of records and pick any obscure fact that takes your fancy - eg the length of the longest sandwich, the weight of the heaviest book, etc.
Otherwise, look through any good reference book, or encyclopedia and pick out dates of obscure events, heights of buildings etc. The point is ( as country boy has stated) is that the answer to the question needs to be 1- not well known and 2- some sort of number, to allow you to allow you to differentiate using a "nearest to" answer. HTH