Isla Muelle was a large island that held a port-colony owned by Spanish. It was located in the South Archipelago. Nathaniel Hawk's ship the Victory was once moored at Isla Muelle after being damaged in a violent hurricane. The city on the island was enormous, even larger than Redmond itself. Though it was the only Spanish colony located in the archipelago, it served as a stop for the yearly Spanish Treasure Fleet which usually resulted in economic boom for the town.
The town, Porto la Muelle, was built into several sectors, seperted by alley ways running parallel to one another. Multiple levels were built on top of each other, and suspended causeways provided easy paths for people to walk across town quickly, rather than talking the lower streets. Bellow the catwalks laid the market square, where merchants came from all over the colony to do trade. There were large gates which lead out to the port in the front of the city, and on the opposite side was the gate leading to the slum district. There were two more portions of the town, the Merchant Quarter, which contained a tailor shop and an HQ for the Spanish equivalent of the East India Trading Company, and the Nobility Sector which held the largest cathedral in the entire archipelago as well as the governor's residence.
You'll notice there's a person aside from the governor in the MuelleTown Hall. If you talk to him and your reputation is at least Bloke, he'll give you a side mission: rescue his captured son.