I like the brutalist bunker feel of KWK Promes' Safe House, a residence outside of Warsaw, Poland. Apparently, the only entrance is the retractrable footbridge. All That Is Interesting called it "The First Zombie-Proof House." From World Architecture News:
The body of the building is a cuboid in which parts of the walls are movable. When the house opens up for the garden, eastern and western side walls move towards an exterior fence, creating a courtyard. After passing the gate one cannot enter the house or the garden any other way but through the main door, waiting in that safety zone, for its opening. The innovation of this consists in an interference of the movable walls into the urban structure of the property. Consequently, when the house is closed (at night for example) the safe zone is limited to the house's outline. During the day, as a result of opening of the walls, it extends to the garden surrounding the house."Safe as houses" (Thanks, Greg Long!)
Accomplishment of this idea required a lot of technically complex solutions. The sliding walls (both 2.2m high, 15 and 22m long) are not the only mobile elements of the building. Apart from these, there are large shutters – all 2.8m high, with width ranging up to 3.5m, and a drawbridge, leading to the roof terrace above the swimming pool. A giant roll-down gate closing the southern elevation also functions as a movie projection screen. All the movable elements are based on built-in electric motors. The whole building is a concrete monolith, while its mobile parts – for the sake of considerable size – are light steel frameworks filled with mineral wool. As a result, the building is excellently insulated when closed. The whole house and all movable elements are finished with waterproof alder plywood. It resembles wood widely found on surrounding houses and barns, which makes it fit well into the landscape.