The Principality of Andorra shares two peculiarities with San Marino. They both have two active heads of state -- the only countries in the world to do so.
And they also are reliant on airport gateways that lie next to their borders, yet beyond them.
Andorra's location, nestled right in the middle of the Pyrenees mountain range, means tourism is key to its economy. Anything that helps bring skiers to its slopes is seen as strategic.
When the construction of an altiport -- an aerodrome in mountainous terrain --was discarded due to technical issues, the obvious alternative was to turn La Seu d'Urgell Airport, just across the border in Spain, into Andorra's air gateway.
This airport, crowning a flat-top hill, had seen little action since regular scheduled flights to Barcelona were abandoned in the early 1980s. However, this might about to change, after the recent completion of a renovation program.
Don't expect big crowds just yet, though. Operational constraints, dictated by the local topography and runway length, restrict operations to aircraft the size of the 27-meter ATR turboprop. However, this may be just enough to bring the airport back to life.
"Plenty of people come to ski to this area from afar. Many of them come by bus and in this context, charter flights can provide a very competitive alternative," explains Jordi Candela, director of Aeroports de Catalunya, the government body that manages the airport. "There is clearly a market opportunity to capture some of this traffic."
Two separate airline startups, aptly named Andorra Airlines and Air Andorra, have launched with the stated aim of serving this market, but none of them has managed to start operations yet.
It remains to be seen whether the market is large enough to sustain regular operations, let alone two competing airlines.
The most famous passenger to have used Andorra-La Seu d'Urgell Airport remains Elton John, who landed here in 2015 on his way to a concert in Andorra.
Liechtenstein
Liechtenstein is another small landlocked European principality with no space for a proper airport.
The closest airport, St. Gallen-Altenrhein, is itself subject to a curious international situation, as it's located right on the Switzerland-Austria border, just a few meters inside Swiss territory but owned and managed by an Austrian company, People's Viennaline.
St. Gallen-Altenrhein Airport made headlines in November 2016 when it became the base of the world's shortest international flight, an eight-minute trip to Germany's Friedrichshafen.
This initiative has already been stopped due to lack of demand, with the last flight taking off in April 2017.
Size isn't everything
Convenient access to air travel has not only become a requirement for a successful modern economy, but also, some might argue, a powerful symbol of sovereignty.
But as you can see, these European microstates prove, each in its own way, that lack of space or a small population is no obstacle to having a vibrant aviation scene or, in the case of San Marino, to become an industry player on a global scale.