Question

To get from Puerto Ventoso to La Colina, you have to take a ferry. The mainland town of Granja Real is 20 minutes by train from Cenador. Manuel can ride his bike from La Colina to Cenador. Which town is on an is

Answer 1

Assuming that the question was "which town is on an island..."

Since you have to take a ferry to either Puerto Ventoso or La Colina, it's safe to say one of these is the island. Since you can ride a bike to La Colina, Puerto Ventoso is the town on an island.