The city's splendid 13th-century castle, probably built by Grand Duke Kęstutis to defend the way to Trakai, was the country's first defensive bastion and the only double-walled castle in Lithuania. The surrounding walls were initially over two metres wide and 13m high. Unlike most other castles of the time this one was made of stone, not wood. However, in 1362, after a siege, the Teutonic Knights managed to destroy it, though legend has it that it was not completely wrecked and that 36 survivors remained. These survivors along with the Knights are allegedly still burning in an eternal fire that can only be extinguished by an innocent person entering the castle via a secret cave. In any case, the ruins' replacement, some of which can be viewed at the site today, was built by 1368. Since then it has been modernised with sleek glass windows enclosing the top and recently got another pricey facelift. Visitors will find a number of fascinating exhibitions, including a history of the castle spread over five spaces within the tower. The dungeons are also worth a visit: slip on a pair of heavy iron chains and find out for yourself what life was like for a 16th-century villain. The castle also plays host to regular exhibitions, concerts and events.