There's no need to pass through immigration and customs upon entering the small state and, in fact, the transition from France to Monaco is so seamless you may not even realize you’ve arrived. Still, for the fun of it, Monaco offers at least two locations for passport stamping: at the tiny tourism office within the train station, Gare de Monaco-Monte Carlo, and at the main Office du Tourisme, a 2-minute walk up the street from the Casino and Hotel de Paris. There may also be an opportunity for a stamp at the Heliport in Fontvieille.
Don’t make our first-timer mistake of many years ago, when we visited Monaco on a Sunday afternoon and found the office closed. No passport stamp for that visit to the principality. For your reference, the main office details are:
Monday - Saturday: 9am - 7pm
Sunday and Holidays: 11am - 1pm
Address: 2 Boulevard des Moulins
The stamp is free, and of a lovely scarlet ink to match Monaco’s flag colors of red and white. No need to return for an exit stamp; one is enough and definitely worth showing off during passport brag sessions.
The main tourism office near the Casino and gardens