Nestled in the corner of the super-block that contains the Tokyo Dome, an amusement park, and other attractions sits Koishikawa Korakuen, a sight I consider a must-see for tourists interested in traditional Japanese gardens.
Be warned that while the text is minimal for each photo, there are dozens of pictures here!
Koishikawa Korakuen is one of the three most beautiful parks in Japan. It's a short walk from Iidabashi Station, Suidobashi Station, or Korakuen Station (though Korakuen Station is the farthest from the entrance). Use the maps just outside the stations and follow the signs to get to the entrance. Note that the sign on the main road from Iidabashi Station is somewhat hidden behind another post.
The park is open daily from 9-5, though it's closed around New Years for a few days. Admission is only 300 yen, a small price to pay for such a beautiful garden.