The harbour at the foot of the fortress hill is the social heart of Lappeenranta in summer. Boat trips depart from here into the Saimaa lake system — everything from short sightseeing cruises to multi-day trips through the canals and channels of Finland's largest lake. The Saimaa Canal, which runs from the harbour south to the Gulf of Finland, was originally built under Russian rule in the 1850s and later rebuilt in the 1960s; cargo ships still use it.
The harbour beach hosts the famous sandcastle competition in July, drawing competitors and spectators alike. The surrounding area has restaurants, ice cream stalls, and the passenger ferry terminal for boats to Vyborg in Russia (service availability depends on current bilateral relations). The harbour promenade is pleasant for an evening walk throughout the summer.