Annual light-up of the cherry blossoms in Chidorigafuchi. One of the most famous night cherry blossom events (yozakura, 夜桜) in Tokyo—700 meters of LEDs lighting the cherry trees on the banks of the moat around the Imperial Palace. The LEDs are turned on around 6pm and switched off at 10pm. Visitors can rent boats during the cherry blossom season to view the trees from the water. Rental is 30 minutes for 800 yen or 1 hour for 1,600 yen and boats are available from 9am to 8:30pm (last admission at 8pm). The nearest station is Hanzomon (Exit 5) on the Hanzomon Line or Kudanshita on the Hanzomon, Shinjuku, and Tozai Lines. The route from Hanzomon moving towards Kudanshita tends to be less crowded. See here for a run-down of other places to see the cherry blossoms in Tokyo.
Event details are taken from official sources whenever possible. It is always prudent to check the official event website before attending to make sure that there have not been any changes. If you know of an error in the calendar, then please let me know through the contact form.