Prague -Cesky Krumulov Day Trip

I would recommend to stay overnight for several reasons. Cesky Krumlov is about 3 hours one way from Prague. It is very touristy during a day. It is magic as it is lit at night and you almost get feeling you have it for yourself when the crowds leave in the evening. And if you do it yourself by public transport including overnight stay it would be still cheaper than guided tour.

There are several bus companies that go between Prague and CK. We used Student Agency. We stayed 2 nights at the Castle View Apartments. Great location and great B&B.

We don't intend to stay overnight, any day tour operators ?

We didn't use a guided tour, but there are several, if you Google. We took Lobo shuttle from Prague.

We did stay overnight, because we were on our way from Prague to Vienna. However, I think a day trip would be perfectly doable, especially at that time of year, when it shouldn't be as busy, as long as you are prepared to make it a very long day with several hours of travel time.

We arrived in CK in the late afternoon (after stops at Castle Hluboka and Divci Kamen). So, we had the evening and the next morning. We found that was plenty of time to see the highlights of Cesky Krumlov, although it was summer, when there are more hours of daylight.

Sorry I can't recommend a specific tour. Maybe do a Google search and read reviews if nobody has any recommendations here.

My husband and I were guided by Kamil Vondrous. It was a privately guided tour, but very affordable. He was wonderful!! I would highly recommend his services.

its small and you don't really need a tour. Bean Shuttle and CK Shuttle both run down and back a few times a day at very reasonable rates.

AND, I agree with Ilja......... 110%

If you must do it as a day trip leave as early as you can. It's quite a distance from Prague.
There are no large motorways/freeways connecting Prague with CK. Expect a lot of traffic...I have driven this route numerous times and have ALWAYS ended up in traffic jams on the 2/4 lane roads. The drive should only take a little over 2 hours but it has never taken me less than 4 because of traffic.
I know that you don't plan to spend the night there but you should seriously consider it. It will be a much more pleasant experience and far less exhausting.

Use a service like CK shuttle that will pick you up where you are staying in Prague and return you there. Weekends are really busy in CK so perhaps go during the week. We took a walking tour that we picked up in the main square. Good value and it covers all the main points. Just bear in mind that it gets dark around 7pm and it gets cooler quickly.

Ditto to Ilja, James E. and Anita's thoughts . . .