"Cotabato City is one of the largest cities in the Philippines, filled with natural landmarks, diverse places of worship, and festivals. Most notable - and most famous to local and foreign tourists - is the Rio Grande de Mindanao, hailed as the second largest river in the Philippines. It's also good to visit the Sultan Haji Hassanal Bolkiah Masjid, the biggest mosque in the Philippines. The Shariff Kabunsuan Festival is a popular and colorful event that commemorates the arrival of Islam in Cotabato."