Tokyo has more or less everything you can imagine, it is a city where it is almost impossible to get bored. The greater Tokyo area is, depending on how you count, the largest or the second largest metropolitan area in the world with a population around 30 million people which is more than the entire population of Australia or the Scandinavian countries. The 23 wards that make up Tokyo proper have 12 million during night and 20 during a workday. People live there all their lives without ever knowing all nooks and crannies of it.
The city is divided into a few districts, from the luxury of Shinjuku to the geekiness of Akihabara and the businesslike manner of Chiyoda. The districts are connected together through an extensive network of trains and subways with the Yamanote, which connects most of the main areas in central Tokyo being the most notable for travelers. You could easily spend years getting to know Tokyo. Assuming however that you have limited time, here are the main attractions.
How to get there
As the capital city of Japan you are likely to fly in to Narita airport when arriving to Japan. From there you can take the train to the center of the city.
Things to do there
A must see for all travelers is probably the Imperial Palace, missing it is a bit like missing Buckingham Palace in London. If you are traveling around Christmas and New Year then do keep in mind that the palace compound itself is partially open on December 23rd (the Emperors birthday) and on January 2nd (to celebrate the new year). You wont get to access the palace itself but you will see the Emperor when he comes out to greet his people. To get to the palace take one of the many trains that travel to Tokyo station and get out at the front gate.
For a view of the city itself go to the newly built Tokyo Sky Tree in Roppongi, the Tokyo Tower near Hamamatsucho station on the Yamanote line or the Tokyo Metropolitan Governmental Buildings in Shinjuku. The last one is free of charge.
If art, culture and stuff like that takes your fancy then Tokyo has plenty of museums, head to Ueno, also on the Yamanote line where you can familiarize yourself with Japanese history, art, culture etc. There is also a Ueno Zoo there, which among other things hosts a giant panda. For those more interested in contemporary Japanese pop culture then the Studio Ghilbi museum might be of interest. This museum is located in Inokashira park, take the Chuo line to Kichiyoji station to get there.
You should also really check out Akihabara, the Mecca of everybody interested in anime, manga, and electrics, the place probably has more stores for the nerd in all of us than any other street in the world. It also has attractive young ladies dressed up in funny costumes and maido cafes (places were you can pay a small fortune for having these girls pour you a cup of tea and talk in a strange manner to you.)
For something a litte more traditional like Sumo and Kabuki you head to Ryogoku Kokugikan or the national sumo hall at Ryogoku station for the former, and Ginza for the latter. Make sure the season is on if you want to see sumo.
Asakusa is another must visit place, located in Taito ward, it is famous for its many temples, the most notable is the Senso-ji dedicated to the Bodhisattva Kannon, it also has no shortage of shopping booths where you can buy all sorts of souvenirs, including replicas of Japanese swords. To get to Asakusa you should take the Ginza subway line from Ueno station. Then there is the Meiji shrine, dedicated to the late Emperor Meiji, built in 1920 it is by far the most impressive Shinto Shrine in Tokyo, seeing it is a must. Take the Yamanote line to Meiji Jingu to see it.
And lets not forget Tsukiji, the famous fish market in Tokyo, you will have to be an early riser to see it in action as the tuna auctions for example start at 5 o clock in the morning. There are also plenty of Suchi bars if you want to try really fresh sushi. Make sure that you consult this site before heading to Tsukiji as public visits are not allowed every day.
Another place well worth seeing and experiencing is Shibuya crossing, it essentially just consist of walking over a street but you probably wont find as many people doing that in one minute anywhere else in the world. It is actually quite a famous landmark, chances are that you have seen it on television. Shibuya is known as the fashion capital of Tokyo, it has no shortage of stores you might be interested in seeing. Near Shibuya, just a train station or walk away is Harajuku, famed for young people dressed up in gorgeously creative ways. Seeing it is a must.
If you like to explore the nightlife of the Japanese capital then Roppongi is a place frequented by foreigners, Shibuya is for the young and trendy while Shinjuku is where businessmen with enough money head to.
There is always something happening in Tokyo, be sure to grap a copy of Metropolis or just visit their site (metropolisjapan.com) to see what is happening when you happen to be there. If you want to experience traditional Japanese festivals look up Japanese festivals on Wikipedia to see what is going on when you arrive. We especially recommend the Hanami (flower watching) festivals in spring when people go out and celebrate the blooming of the cherry blossom or Sakura as they are called in Japanese.
As we already said Tokyo alone could keep you busy for years, however if you have limited time you might want to head out of this concrete jungle and see more of Japan. The Shinkansen (or bullet train) is your fastest way out, in fact you should not leave Japan without trying it at least once.