Taking the bus — what you need to know
Three companies run the route and all three are comfortable modern coaches, not the rattling minibuses people sometimes imagine. RegioJet is the one most travellers rate highest: reserved seats, wifi, a steward serving drinks, and fares that start low if you book a week or two out. FlixBus and Leo Express cover the same route at similar times.
The catch is that they leave from different places in Prague. RegioJet services generally go from Na Knížecí; FlixBus mostly uses Florenc, the main bus station, which is the most central and metro-connected of them. Check your ticket rather than assuming — this is the single most common mistake on this route.
Book ahead between June and September and over Christmas. This is one of the busiest tourist corridors in the country and the cheap fares disappear first. The bus sets you down at Český Krumlov's bus station, which is a five to ten minute walk downhill into the old town.
Why the train is the weakest option here
Czech trains are generally excellent, which makes this route the exception that catches people out. There is one direct service a day, leaving Prague's main station in the morning and arriving in Krumlov about two and a half hours later. It is a pleasant ride.
Miss it, and you are changing at České Budějovice onto a local service, which pushes the journey past three hours for more money than the bus. Unless you hold a rail pass or you have a strong preference for trains, the coach is simply better on this corridor.
One practical note on arrival: Český Krumlov's railway station sits above the town, about a twenty-minute walk down — fine with a daypack, less fun with a suitcase on cobbles.
Day trip or overnight?
Krumlov can be done in a day from Prague, and a great many people do. But it is worth knowing what a day trip costs you. The town centre is small and it fills with coach groups between roughly eleven and four, which is precisely the window a day tripper occupies. Stay the night and you get the place at dusk and at breakfast, when it is quiet and genuinely extraordinary.
If you only have the day, going by car is what makes it comfortable: leaving at eight rather than on a coach timetable, and being driven back when you are ready rather than at the last departure. A private day trip has the driver wait, so your day is as long or short as you want it.
If you are staying over, the one-way transfer or the bus both make sense — and many travellers carry on south to Austria from Krumlov rather than doubling back to Prague.
Stops worth making on the way
The drive south runs through South Bohemia, and two stops are close enough to the road to add without lengthening the day much.
Hluboká nad Vltavou is the white neo-Gothic castle that appears on half the postcards in the country — often described as the Czech Windsor, and about twenty minutes off the direct route. České Budějovice, the original home of Budweiser beer, has one of the largest town squares in Europe and makes an easy lunch stop.
Neither is possible on the bus or the train without losing hours to connections. If either appeals, that is one of the better arguments for taking a car — with a private transfer the stop is arranged when you book and costs nothing extra.
Carrying on to Austria
Český Krumlov sits close to the Austrian border, and a large share of visitors do not go back to Prague at all — they continue to Vienna, Salzburg, Hallstatt or Linz.
Public transport for that leg is awkward: it usually means backtracking to České Budějovice or Linz and changing. By road, Krumlov is a natural halfway stop between Prague and Vienna, and adding it to a Prague–Vienna transfer costs far less than treating it as two separate journeys.
If that is your plan, book the through journey rather than a one-way to Krumlov and a second trip afterwards.