Corregidor. This is a rock mountain in the channel leading from the South China Sea into Manila Bay. After the Magellan exploration, the Spanish returned to colonize the Philippines. They built the first fortresses on the rocky island. Even by 16th century cannon, that made it hard for a wooden ship to enter Manila Bay.
The first big trade thing that happened in Manila was that it was the “silver concentration point” for purchasing Eastern spices and such. The silver mined in Mexico (centered around Taxco) was shipped overland to a nice port on the Pacific (Acapulco) and then to Manila.