Every one knows that archeological stuff has to be dug up. Buildings get buried over time.
This has happened with Oxford's unique sunken Cathedral. Over time this Cathedral has become buried, and now only the "spire" (at waypoint) is visible above the ground. However the building itself is intact and can be accessed nearby. There are separate male and female entrances to the cathedral. The cache, a black nano, is placed near one of the entrances.
Note: The above is entirely fiction, but is a favourite story of students to tell to tourists wanting to see some history. The spire itself is a memorial to the Oxford martyrs (see also GCJ170).
FTF: Jammy&Badger 23rd July 2013