Possible Clues:

• Record for posterity the Spanish University's opening with German backing
• Where one might find a date ... with a hint to this puzzle's theme
• *Chill pill?
• Site map clue must be solved to show buried receptacle?
• Buried historic cache
• Box buried today to be found some time in the future
• Historic cache for the future
• “To be opened in 50 years” cache
• What may be kept in a cornerstone
• Container buried with items to be discovered in the far future