The official opening Tuesday of Johns Hopkins Hospital's two 12-story towers will mark the final step in the largest hospital project in Maryland history. The facility, in the works since the 1990s, will change the way Hopkins practices medicine. Construction of the 1.6 million-square-foot facility with 560 private rooms was a five-year undertaking. The move of nearly 350 patients, which will be completed Monday, required similar precision in planning and execution. Over two years, staff took training courses and participated in several mock runs, with volunteers playing patients, to prepare for the real event.