One of the biggest problems with putting all this in a single location is that, no matter how secure the location is from the elements, it is not secure to people (or else it would be useless).

Given the length of time imagined, I think the odds that the place is accessible by individuals or groups who believe they should destroy the data approaches 100%.

See the deliberate destruction of ancient sites all across the Middle East. See the sacking of Rome by the Vandals, the *goths, and the Normans. See the destruction of the Library of Alexandria. See the rise in religious extremists who seem specifically to hate artifacts belonging to other cultures on their soil.

How does a physical repository of human knowledge defend itself against this?