Architect John Hix—who, as one might gather, worked under renowned American architect and concrete aficionado Louis Kahn—designed the hotel Hix Island House in Vieques, off Puerto Rico. The latest guest house on the property is called Casa Solaris and is entirely removed from the commercial grid, running completely on solar power. Photo by Michael Grimm. Tagged: Exterior, House, Concrete Siding Material, and Flat RoofLine.  Photo 1 of 10 in Find Yourself in Paradise at These 10 Modern Rentals in the Caribbean from Modern Concrete Getaway in Paradise