The Greater Tokyo Area is actually the most populous metropolitan area in the entire world, a 2016 estimate put the total population of the area at 38,000,000. Shinjuku Station alone has an average of 3.5 million people passing through it on a daily basis. This can make Shinjuku Station seem like a maze at first, but once you get used to the pace of the city it feels normal.
Tokyo has something for everyone, literally. You could go watch the traditional sport of sumo wrestling in the Ryogoku Kokugikan in Sumida, or go and eat crazy coloured food while surrounded by bright lights in the Kawaii Monster Café in Harajuku. The city moves at a fast pace, but you can move at your own pace within it.
Nestled in Sumida you can find Tokyo Tower, which is the tallest tower in the world. It stands at a grand 634-meters high, and from the viewing deck, you can see nothing but the city of Tokyo surrounding you. There is even a glass patch to stand on if you are brave enough to see the drop beneath you.
You can find one of the most famous temples in Tokyo in Asakusa. It is called Senso-ji, and it is actually the oldest temple in Tokyo. It was founded all the way back in 628 after two fishermen found a small golden statue of Bodhisattva Kannon in the Sumida River. It is estimated that 30 million locals and tourists visit the temple on a yearly basis. To get to the temple you will have to walk up Nakamisedori Street, which is lined with shops that sell a mixture of traditional snacks and souvenirs. Be careful, if you buy ice cream in the summer you do have to eat it inside of the shop!
As a city, Tokyo can be anything that you want it to be. If you would like to relax and enjoy the temples of the city then you can, and if you want to enjoy yourself in the lights of Shinjuku, then you can do that too.