Lake Plateliai (Samogitian dialect: Plateliu ežers) is the biggest lake in Samogitia and 9th biggest in Lithuania. It is the central attraction in the Žemaitija National Park. It covers about 12 km² and reaches up to 47 m in depth. It has seven islands, one of them housed a castle and now is called Castle Island. Archeologists found remains of two castles and think it might be the Queen Bona castle. The lake has both diving and yacht clubs. Plateliai town is located on the west bank of the lake.
Lake Plateliai is famous for several events. It hosted rock music festival Roko naktys (English: Nights of Rock) since 2002. However, it seems the festival will have to relocate as the little town cannot accommodate more than 4,000 people attending the event. For 25 years swimmers have competed in a marathon in the lake. In 2006, a record number of people participated: 21 people swam a distance of 3.5 km and 154 of 1.8 km.
The lake is one of the most interesting for underwater archeology. Scientist think that the water level was much lower years ago and some islands are now underwater. For example, in 2002 divers found a big stone with human-made markings, that resemble the letter L. The stone was surrounded by smaller stones and a hypothesis was raised that it was a sacred place for the pagans. In 2002, on the bottom of the lake archeologists found three boats, about 5.5 meters in length, dated to the times of Vytautas the Great.
The Cold War Museum was established in the Plokštinė missile base, located in the forest not far from the lake.