Although San Marino welcomes 2 to 3 million visitors a year, I am the first one on this website to give my review. Where do all these millions come from, one wonders? Probably they were on a day trip from the nearby seaside resort of Rimini. My visit was on a weekday in February and there surely weren't many people around at that time.
I started my visit with a hike along the ridge of Mount Titano. This path, starting from parking lot P3, takes about one hour and passes all three towers that San Marino is famous for. A fine but steep walk. There even still was some snow on the ground!
I went to the interior of the middle of the three towers, Castello della Cesta. It has a weaponry museum (as castles all over the world so often have). The views however from the top of the castle are splendid: on San Marino town and on the surrounding snow-covered Apennine Mountains.
The track ends at one of the city gates of the historical centre of San Marino. The centre is full of souvenir stalls and restaurants. It has a distinctive layout, with all streets running east-west above each other. I walked around for a bit and rested awhile at San Marino City's major landmark, the Palazzo Publico.
That's about all there is to see here, in this very debatable WHS. ICOMOS praises its link between tangible and intangible heritage (freedom, representative democracy, republican government). In the Advisory Body evaluation, San Marino however is compared to about a dozen other places, varying from Assisi to Singapore. Personally, it reminded me a lot of Bellinzone (which also has 3 castles in a mountain setting).