A magnificent monument of Gothic architecture, the cathedral started off as a humble chapel built in the 7th century by Omer on the site of a cemetery for Saint-Bertin monks. Raised to the level of a collegiate church, it was enlarged on two occasions before reaching its current proportions. One of the most interesting things inside is Saint Erkembode's tomb, worshipped by the faithful for walking on and on in his mission to spread Christianity. As time went on, people started praying to this saint to protect their children against walking problems, which is why you'll see lots of little pairs of shoes on the tomb. it's definitely worth taking a good long look at the fabulous astronomical clock from 1555, which is one of only two in the whole world.