One day
Start early in the old town before the coaches — the main square, St Vitus Church and the cobbled lanes — then cross to the castle for the courtyards, the painted round tower (climb it for the view), the bears in the moat, and the terraced gardens. Have a Czech lunch and a South Bohemian beer, take a riverside stroll or a short raft on the Vltava, and end with the lit old town at dusk once the day crowds leave.