Its guaranteed to keep you alive for 6 months and survive at 20 megaton blast - not too shabby:
Here is a bit about Terra Vivos (from their homepage):
Vivos is a privately funded venture, with no religious affiliations, building a global network of underground shelters, to accommodate thousands of people. Vivos will provide a life assurance solution for those that wish to be prepared to survive these potential events, whether they occur now, in 2012, or in decades to come. Co-own an equity share of the Vivos shelter closest to your home area. Which side of the door do you want to be on?