So many favourites, but going to go with the most memorable, well two most memorable actually.
One is called TARDIS and the other called DALEK, both puzzles located on the northside of Brisbane Australia. There was a small puzzle for each to gain the coords, however the final for each was just what the names would imply from Doctor Who, Dalek I imagine was life size, and Tardis was smaller, however two very good caches.
Cheers
Joel - OrionJ