The last time I visited Ameyoko was a couple O years ago - should probably visit more often as the food is great and there is lots (and lots) to see.
Also wrote up a post on Ameyoko back in 2008 which lives here - going to cheat and copy/paste bits of it.
Located between JR Okachimachi and Ueno station is Ameyoko - an outdoor shopping market filled with many dealers wheeling and dealing discounts on all kinds of stuff including seafood, sweets, t-shirts and snacks. Map of Ameyoko below.
"Ameyoko" [アメ横[あめよこ]] is short for the full name of the market which is "Ameya Yokocho" [アメヤ横丁[あめやよこちょう]]
Many moons ago, American soldiers used to come here to sell their bits n pieces to make a few yen on the side.
One of the origins of the name "Ameya" is said to come from "AMEricans" and "YA" meaning "shop" = American shop.
Another explanation of the original meaning of "Ameya" is said to come from many shops in the market that sold sweets. "Ame" meaning "sweets" and "ya" meaning shop.
The whole area around Ameyoko is filled with side streets which branch off all over the gaff. Somewhere in here you can make some dog tags of your 2D girl/boyfriends, buy some frozen pigs ears to bring back for your nephew, stock up on old military equipment so that you can get treated like a criminal while going through security checks at the airport and you can also stop by the many stalls selling hot n cold snacks to keep you going.
While there are many foreigners who visit Ameyoko, many locals come here to do their daily shopping which makes this place special in that you also get to see a slice of life in Japan.
Previously however, Ameyoko wasn't so much about "A slice of life" - rather a "Slice of somebody's knife." After the Second World War, Ameyoko became a black market where a load of rogue soldiers and gangsters would come to wheel n deal and occasionally shoot others.
The authorities at the time turned to a business man called Hirokichi Kondo and asked for his help to buy up 80 stores in the Ameyoko area with the main purpose to drive out the trouble makers. Over time, Ameyoko started to become a safer place to be.
Ameyoko is in the Ueno area which is also close to Akihabara. If you are nearby then I recommend dropping by - don't go too late (8PM) or many stalls will be closed.
Just a few things to mention before I hit the sack. Currently creating a Places to visit in Japan guide which you may want to refer to before you come over.
You can also see a PDF icon on some posts which we are testing at the moment - Mirai Gaia can now generate a PDF of each post so that you can conveniently read it on your mobile device or if you are using an iPhone/iPad or iPod Touch then you can view the posts in iBooks. Download the PDF for this post and give it a whirl - lemme know what improvements you want. Font sizes are 16px so that they should look decent on the iPhone 3GS.
Also plan to release an RSS feed so that you can grab all the PDF's for each category. Want to make the whole site archive-able in PDF format. Will probably torrent each years worth of posts in PDF format too.
You will also see a little map icon in the gray bar below the title - hover to get Geocodes or click to see the location in Google maps. Soon there will be a map of Japan filled with all the thumbnails for posts on DC.