time capsule 
noun
A container storing a selection of objects chosen as being typical of the present time, buried for discovery in the future: the opening of a time capsule dating from 1904 the house had stopped in time, like a time capsule...
- On Monday, they'll bury a time capsule containing work from every child in the school - to be reopened in 2013.
- Very soon, a vast time capsule will be buried containing all manner of goods and items intended to wholly embody 20th century life.
- A window to the past was opened by pupils at a Yorkshire school yesterday, after the discovery of a time capsule dating back to 1891.