Mahmut Bey Mosque is Kastamonu's strongest single sight. Built in 1366 in Kasaba village, it belongs to the medieval Anatolian tradition of timber mosques and is famous for its nail-free wooden construction.
The outside is plain, but the interior is the reward: wooden posts, painted surfaces, and a warm, handmade geometry that feels very different from later Ottoman stone mosques. It is outside town, so plan transport rather than treating it as a casual stroll.