The Old U.S. Customs House on Morse Street is now a small museum focused on Samuel Morse, the Morse family, and Arroyo's place in the early history of telegraphy in Puerto Rico. The building is also tied to the island's American customs administration after 1898.
It is a modest stop, but it gives Arroyo its best historical thread. Pair it with a walk through the plaza and the waterfront rather than treating it as a standalone museum day.