a castle, a thousand-year-old Benedictine monastery, and a botanical garden initially started by Maximilian I of Mexico in the 19th century. Peacocks and peahens still roam the isle, descended from the original peafowls brought over by Maximilian. The nearby islands include the historical island of Korčula. The Catholic inhabitants of Korčula keep alive old folk church ceremonies and a weapon dance, the Moreška, which dates back to the middle ages. Originally danced only on special occasions, in modern times there are performances twice a week for tourists. The main town's historic sites include the central Romanesque-Gothic Cathedral of St Mark (built from 1301 to 1806), the 15th-century Franciscan monastery with Venetian Gothic cloister, the civic council chambers, the palace of the former Venetian governors, grand 15th and 16th-century palaces of the local merchant nobles, and the city fortifications. Further along the Adriatic are the forests of Mljet island. Over 72% of the island of is forest. Its geological structure consists of limestone and dolomite forming ridges, crests and slopes. A few depressions on the island of Mljet are below sea level and are known as blatine ("mud-lakes") or slatine ("salt-lakes"). During the rain seasons, all blatine are filled with water and turn to brackish during dry seasons. Central and Northern Croatia The northern part, with the hilly area of Zagorje and Međimurje, is dotted with castles and spas, and the old city of Varaždin. In Međimurje, there are spas and facilities for recreation in Vučkovec and around Sveti Martin na Muri, both in the northern part of the county and near the Mura. There are also more than 200 clubs for various sporting and recreational activities such as mountaineering, fishing, bowling, CB radio, parachuting and flying small aircraft, including unpowered gliders and powered hang gliders. Hunting also attracts numerous hunters in low game and birds. In Čakovec Castle, there is a Međimurje County Museum and an art gallery. In the chapel of Sveta Jelena in Šenkovec, and in the Church of St Jerome in Štrigova, there are Baroque frescoes of Ivan Ranger dating between 1776 and 1786. Prelog is home to the beautiful Church of St James, built in 1761. Varaždin, with its monuments and artistic heritage, represents the best preserved and richest urban complex in continental Croatia. The Varaždin Old Town (fortress) is a medieval defensive building. Construction began in the 14th century, and in the following century the