Lappeenranta (läpˈpānränˌtä) [key], Swed. Villmanstrand, city (1998 pop. 57,374), Southern Finland prov., SE Finland, on Lake Saimaa. It is an important trade and industrial center, with sulfuric acid works, lumber mills, and cement factories. There is a hydrotherapy center (est. 1824) in Lappeenranta. The city was chartered in 1649 and became an important border fortress after the Treaty of Nystad (1721).