Isola Sacra is a flat, triangular island at the mouth of the Tiber, cut off from the mainland by the river's natural channel, the Fiumara Grande, and by an ancient canal dug under the emperor Trajan. Most people know the area only because Rome's main airport, Leonardo da Vinci, sits just to the north, but the island and its surroundings hold a remarkable amount of history if you are willing to pause for it.
This was the site of Portus, the great imperial harbour of Rome. The emperor Claudius began building it in the first century AD because the old river port at Ostia could not handle the enormous grain ships coming from Egypt and North Africa, and Trajan added a hexagonal inner basin whose outline is still visible today, now a lake inside a park near the airport. On Isola Sacra itself lies the necropolis of Portus, a cemetery of brick tombs with inscriptions and reliefs showing the trades of the people buried there: millers, doctors, shipwrights. Across the river, the ruins of Ostia Antica are among the best-preserved Roman towns anywhere.
Fiumicino town, on the northern bank of the canal, is famous among Romans for its seafood restaurants, and people drive out from the city specifically to eat fish here. Grilled or fried, spaghetti with clams, or a simple plate of anchovies, it is all very good, and lunch by the water is a fine reward for a morning ride. The island side is quieter and more residential.
As riding goes, this is flat coastal country, with straight roads, roundabouts and plenty of traffic, especially around the airport and on summer weekends when Romans head to the beaches of Fregene and Ostia. The roads are not always in good condition, with potholes and patched surfaces, so keep your eyes open. Fuel, food and everything else are easily available. The sea breeze can be refreshing in summer but strong in winter, and in the evenings the sunsets over the Tyrrhenian Sea can be spectacular. Inland, the roads soon lead to the hills, where the Castelli Romani wait.