Laavu, a traditional Finnish shelter any passerby may use. Will build my own one day. We have used the American version in the Cascades while snowmobiling . They are usually found stocked with basic supplies for a few days survival if needed.
The idea of building an underground house has been around for a long time because it is a great idea. With the right technique applied this shelter can keep you warm in the winter time and cool in the summer time, with little to no electricity.