The city is somewhat close to Pisa so it can be reached by plane, Pisa's international airport being just 20 kilometers away from the Viareggio city center. So keep in mind that if you visit Pisa you can easily do a day trip to the Tyrrhenian Sea coast and visit Viareggio.
There aren't many classical tourist attractions in the city but if you are in the mood for a walk on the seaside or spending some time on the beach Viareggio is perfect: not that crowded and with prices that can match any budget.
Let's see some pictures of what Viareggio has to offer: