The nation’s capital is famous for its stately hotels, palatial brick and limestone piles with paned windows framed by passementerie-laden curtains. The Conrad Washington DC, part of the luxury portfolio of Hilton, brings a vastly different design approach—a modern elegance—with such distinctive features as floor-to-ceiling glass walls in the guest rooms, a soaring, sinuously curved skylit atrium, landscaped terraces adjacent to a bar and a café on the third floor, and a roof garden topping its 10 stories.