This is an excerpt from the Eating chapter of Lonely Planet's Tokyo guide.
It’s hard to imagine how Tokyo could function without noodles. From traditional Japanese staples such as soba and udon to that much beloved Chinese import that is rāmen, Tokyoites slurp down an impressive amount of noodles in their daily lives. Noodle shops run the gamut from tachikui (立ち食い; stand-and-eat) noodle bars in train stations and corner places where you purchase a ticket in advance for your meal (usually these places have picture menus) to highly refined restaurants with gorgeous pottery and gardens.
Soba are thin, brownish buckwheat-based noodles, while udon are thick, white wheat noodles. Soba is more closely associated with the Kantō region, which includes Tokyo, while udon are more reminiscent of Kansai (around Osaka). With that said, the vast majority of restaurants throughout the country serve both. Here are a few serving styles you may find.
Kake-soba or kake-udon is served in a large bowl of light, bonito-flavoured broth.
Mori-soba (aka seirosoba) or mori-udon is served cold and piled on a bamboo mat; very refreshing in warm weather.
The most popular type of cold noodles is zaru soba (or zaru udon), topped with slivers of dried nori (海苔; seaweed). It comes with a cup of cool broth and small plate of wasabi and sliced spring onions – stir a bit of these at a time into the cup of broth and eat the noodles by dipping them in this mixture. Do not pour the broth over the noodles – it creates a huge mess! At the end of your meal, the server may give you a container of sobayu, the hot water used for boiling the noodles, to mix with the leftover broth, which you drink like tea.
Rāmen originated in China, but its popularity in Japan is epic. Your basic rāmen is a big bowl of noodles in broth, served with toppings such as chāshū (sliced roast pork), moyashi (bean sprouts) and negi (leeks), though you can expect to see anything from Hokkaidō butter corn and fresh seafood to wontons and Chinese vegetables. Although you may be a loyal rāmen devotee in your own country, we can assure you that instant noodles in the West are a poor preparation for the deliciousness that is real rāmen.
Note that although it’s highly rude in the West, in Japan it is customary to slurp your noodles, both to cool them (when hot) and to enhance the flavour.