Udon is a kind of thick wheat flour noodle. It is served either with hot or cold soup. Its soup is different from the soup of ramen. Its soup is not oily. It is made from soy sauce, dried bonito, and etc. It is usually topped with a chopped spring onion. Other common toppings are tempura or aburaage, a type of deep-fried tofu pockets as shown in the picture. The flavour of broth and elasticity of noodle vary from region to region. Dark brown broth is used in eastern Japan, and light brown broth is used in western Japan. Compared with other regions, noodles in Shikoku region is more elastic. I recommend you to try udon with several toppings.