Lake Galvė is the largest and most beautiful of the several lakes surrounding Trakai, and it is the body of water on which the Island Castle sits. The lake covers about 4 square kilometres and reaches a maximum depth of 47 metres — unusually deep for a Lithuanian lake, and clear enough for swimming in summer.
Paddleboats and kayaks can be rented along the shore near the footbridge to the castle. Circumnavigating the lake by kayak takes two to three hours at a leisurely pace, offering constantly changing views of the castle from different angles. In summer the water temperature reaches 20°C and swimming directly from the small beaches along the shore is entirely comfortable. Ice fishing is a winter tradition when the lake freezes.