Amazon has unveiled the latest design plans for the second phase of its $2.5 billion Arlington HQ2 campus. The proposal for the PenPlace site includes three 22-story office towers, several smaller buildings, a 250-seat outdoor amphitheater, public green space, and a fourth 350-foot swirling glass tower as the development's centerpiece. The second phase of this proposal could break ground as early as 2022 and complete construction by 2025 if the approval process goes as planned.