1966. Herman's Hermits released an album called Both Sides. On it, at least on the UK version, they took an old song from 1937 and made it their own. If you know the song, you know the location of the cache. If you don't know the song, have a listen: https://www.youtube.com/watch?v=8vZfESePu94
But be stealthy, in case a certain little lady comes by, as they say. She may be fabulous and beautiful, but she's likely a muggle. Oh me, oh my.
As always bring your own writing implement, and and a TOTT might be required too, one that is found in many ladies' make up kits.