Twin Cape is located at the bottom of Reverse Mountain, at the exit that leads into the Grand Line. The area is located precisely where the Red Line and the Grand Line meet. From this place is where one can choose one of the seven routes of the Grand Line by waiting for the Log Pose to set on the desired one.
The lighthouse is located at the bottom of reverse mountain, where one can find information about the dangers of the Grand Line. This is the where the Reverse Mountain Arc took place. Crocus has been the caretaker for at least fifty two years, taking care of Laboon as well, minus the three years he spent as the doctor of the Roger Pirates. There's a lighthouse on both sides of the entrance, and Crocus appears to reside at the northern one.