Only one reason to go to Pisa, yes? Well, two at a pinch - the airport and the Leaning Tower.
Sad but true - many people experience Pisa only as a small airport (small but very, very busy - it's pretty much the gateway to Tuscany, Umbria and the rest of central Italy). Perhaps it's somewhere you'll need to spend a night due to an early flight or a late arrival, and then off to the motorway or the train station you go.
The real Pisa is actually a lively and interesting place (largely thanks to the University and associated research centres), and yes, the Leaning Tower (and enclosing Campo dei Miracoli) really IS the definition of a must-see.
Pisa may no longer be a port (it now lies inland), but it was at one time of the pre-eminent powers of the Mediterranean, having its golden age as a maritime republic during the eleventh and twelfth centuries. The architectural style of 'Pisan Romanesque' is on show throughout Tuscany, often manifested in the splendid two-tone marbled churches of the region.
The city was spared little - by either side - during WW2, and the Camposanto cemetery was effectively beyond rescue. The breathtaking grouping of the tower, the cathedral and the baptistery were spared, mercifully, and it is here that the crowds are headed. Just how close the tower came to tumbling is amazing and borderline scandalous, but it has now been secured for a good few decades at worst. It is once more open to visitors.
The Arno river neatly dissects Pisa, with the airport and the railway station to the south, with the bulk of the 'sights' being on the north side. A great time to visit is the end of June, with the spectacular Gioco del Ponte taking place on the last Sunday of the month.