Tokyo is a massive city and figuring out where to start can be overwhelming. To get you going, I recommend a half day in Asakusa. Located in the “low city”, Asakusa is home to Sensoji, a 7th century Buddhist temple. The temple is an easy 5 minute walk from Asakusa station and is accessed by a walking street filled with vendors and food. (Note: The area can easily be accessed by several other subway stations as well). You will pass several other gardens, shrines and temples from the same era in the area. Make sure to walk through the park to the left of the temple and see Tokyo’s oldest stone bridge.
If in Tokyo in mid-May, definitely visit the area for the Sanja Masuri (Three Shrine) festival which celebrates the founding of the temple in 628 AD by two fisherman brothers.
Across the street from the walking street and Kaminarimon (Kaminari Gate) there is a tourist office. If you go to the top floor (free) you can get wonderful views and photos of both the temples and the new Tokyo Sky Tree.
A short walk away is the river and the Asahi Beer Tower, home to several breweries. The building is unmistakable with the signature Flamme d’Or on the roof. But truth be told, I think it looks more like a golden sweet potato.
Japan’s tallest tower is also in the area. It is easily accessible via subway or a short 30 minute walk. From here you can pay to go up the tower for the views or just hang around the mall and shop.