Don Quijote or "Donki" is the place to go to buy just about everything! It's a discount store which sells electronics, clothes, costumes, makeup, sports equipment, snacks, food, drinks, games, bicycles, etc. and they are all a little cheaper than buying them somewhere else. And, they are open way past midnight!
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The stores are all packed to the brim and it's like a maze inside. Finding what you want could be a little bit tricky, because the aisles are so narrow and the shelves are so tall, but you can bet that you will find something else you want on the way to whatever you're trying to find. What they have in each store is a little bit different according to it's size, so if you can't find what you want at one store, try another one.
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Donki has stores all around Japan, and there are more than 30 stores just in Tokyo. They even have one in Hawaii! You can find Donki in any one of the large cities in Tokyo, but if you're in Akihabara, and are planning to go to the electronics store, try exploring the corners of the city and stopping by Donki first. You might be able to find a better deal!
Access: Akihabara Station
Address: 4-3-3 Soto Kanda, Chiyoda-ku
Tel: 03-5298-5411
Business Hours: 10:00AM-5:00AM next day
Check out their homepage in English, Chinese, and Korean.