Nijubashi(which means the "Dobule Bridge") is one of the most well-known bridges in Japan. If you are looking at the bridge from the front, the two separate bridges appear as a single two storied bridge.
Nijubashi bridge is only opened on special occasions such as for official state guests and for holding formal ceremonies at the Imperial Palace.
On my first day in Tokyo jet lag woke me at 5:30am, so I got an early start and walked around the grounds of the Imperial Palace.