Investing $100k into physical gold (bars or coins) is the most prudent option; given the state of economic turmoil worldwide.
Take a look at the long term charts; they're pretty self explanatory. Gold has an upward trend for 100+ years.
A more high risk/high reward investment would be to buy $100k of physical silver. Silver has a similar track record and inherent benefits of gold. Yet, with a combination of factors that could make it even more bull than gold (ie- better liquidity, industrial demand).
Beyond that, you may want to look at other commodities such as oil and agriculture.
The point is, this is troubled times for worldwide economies. Times like this you want to invest in REAL things like commodities or companies that are actually producing essential materials.