Oplenac, in the town of Topola, is where Karađorđe plotted the Serbian insurrection against the Turks in 1804. One ticket grants access to all attractions, including King Peter's House (with the royal family's portrait gallery), Karađorđe's Fort (now a museum housing period artefacts and personal effects), Karađorđe's Church and the Winegrower’s House (now a gallery). The most impressive is the white-marble Church of St George, adorned with magnificent mosaics made from 40 million pieces of coloured glass; its crypt is the Karađorđević family mausoleum.
Other sights scattered within walking distance are Karađorđe's Barracks, the King's Villa and the Queen's Villa. A short drive away is the King's Winery, where you can see original equipment in a small permanent exhibition.
Buses connect Topola with Belgrade (660RSD, 1½ hours, 11 daily).