Cap d’Ail near Monaco is one of the best places for just such a trail walk, it is also one of the most calming and beautiful places in the French Riviera. And here you have a couple of options, you can head towards Plage Mala (beach) while taking in all the amazing scenery along the way, and then, if you felt like it, you could follow back along the same Mala coastal footpath (Le Sentier du Littoral) and walk into the Principality of Monaco in no time at all.
Arriving to Cap d’Ail by train (the last stop before Monaco coming from the direction of Nice) seems to be the most convenient way to travel as finding a parking spot can take forever, especially during high season.
Stepping off the train, you will notice Cap d’Ail is a very quiet, almost heavenly location. Make your way behind the train station and turn left to exit the grounds.
Personally, I find Cap d’Ail and Plage Mala lovely places to visit any time of year!