This is a wonderful waterfront trail just west of Monaco. A paved off-road path (‘Sentier Littoral/Bord de Mer’) runs for about 2.5 km between Mala and Cap d’Ail, featuring the Cap de Mala, Cao Rognoso, and Cap d’Ail. Gorgeous water views the whole way, and one of the flatter routes in the area. Might be crowded with walkers, but very runnable, especially early or late. Beautiful sunrises! There are several beaches in the area — Plage Mala or Douaniers — if you’d like to take a dip.
For an add-on, pop up to the main road and head into Monaco. Note that some of the roads in this area are very narrow and might not have sidewalks. There’s also a train station in Cap d’Ail, so you can use that for a one-way run and head east toward Nice or west to Monaco.