The soup is what makes it special. The cook simmers beef bones and meat for many hours - sometimes a whole day - along with soy sauce, ginger, garlic and Chinese five spice. The broth slowly turns deep brown and starts to smell amazing. By the time it is ready, the meat is so soft you could cut it with a spoon.
Every restaurant has its own secret recipe. Some are spicy, some are mild. Some add tomatoes, some add radishes. Some are clear, some are dark and thick. Some families have been making the same recipe for generations, passed down from grandparent to parent to child without writing anything down.
Noodle eating in Taiwan has its own rules. You hold chopsticks in one hand and a soup spoon in the other. Lift noodles with the chopsticks, scoop a little broth with the spoon, and slurp - yes, slurp! Slurping noodles is polite in Taiwan. It cools the noodles down and shows you are enjoying the meal.
Taipei City Government holds a 'Beef Noodle Festival' every year where chefs compete to make the best bowl. Judges taste dozens of soups in a single afternoon. The winning chef becomes famous across Taiwan, and people queue at their restaurant for months afterwards.