Cresky Kromlov or Dresden

Daytrip from Prague to Dresden isn't sensible, because Dresden is so easy to get to on the train while in eastern Germany. They are not, even remotely, comparable cities. Cesky K is a small medieval town lost in the sands of time, some say too touristy but I like it a lot - especially the Baroque Theater. I find the Castle (really, mansion) underwhelming.

Dresden has some of the most important wall-art in Germany. Also a great opera house, and lovely wiederaufbauen architecture. Fabulous museums, including two unique Decorative Arts museums (i.e. beloved to painting-haters ... ) called the Green Vaults.

Dresden happens to be on a river that has river boats almost to Czech Republic. This would be more interesting than driving, but I haven't done it - only a boat daytrip out and back to Dresden.

The two places are quite different, and I can't say I fell in love with either one. if you like museums at all, I'd pick Dresden in a heartbreat. I'm not really a "museum person" but still went to a few in Dresden - despite my short attention span, I still enjoyed the portrait gallery in one of the museums. Other than the baroque theater in Cesky Krumlov, otherwise it's just a charming little town with a lot of tourists now.

One thing super interesting about Dresden: the buildings in the center are generally HUGE - like oversized to what they look like that ought to be - and quite impressive.

Cesky Krumlov does offer white water rafting and canoe trips down the river in the warmer months, if that interests you.

None of them is good for a day trip. Roundtrip to Cesky Krumlov takes 6 hours. Round trip to Dresden 4 hours. You won't have enough time to enjoy this relatively big city.

A more realistic day trip from Prague is Tabor, only 1,5 hrs from Prague main station (Praha hl.n.) on fairly regular direct trains.
Look at the Wikipedia page for what's on offer. And use this train planner for the connections (no need for advance buying of tickets; do it at the railway station).

I lived in Prague for a couple of years so will make a few other suggestions. It is very easy to get mini bus tours from Prague so there is plenty of opportunity to get places that you might not be able to without a car. I would suggest Kutna Hora. It is a small Czech town so very traditional and the bone church is the highlight. Karlovy Vary is a beautiful old spa town and the drive is very pretty as it sits on the edge of a national forest. Another trip would be to nearby Terezin. This was a concentration camp which is still largely intact and the whole town of Terezin was actually essentially turned in a ghetto during the war. Ceske Budejovice is also a lovely little town on the way to Cseky Krumlov. Like a smaller version of Prague.

That is not to deter you from Dresden which is about 2 1/2 hours on the train. Keep in mind that Dresden was heavily bombed in the war so everything is fairly new. Either built in the Soviet era (astoundingly ugly), within the last 15 years or is a rebuilt version of an older building. But there are still buildings from before the war. The Meissen museum is worth seeing. My recommendation would be see something more of the Czech Republic.

Absolutely agree with donnamartinukusa. If you go to Karlovy Vary go also to nearby Loket. Somewhat resembles Cesky Krumlov but without tourists.

Hi,

Are going to have another opportunity to see Dresden on this trip? If not, then take day trip from Prague to Dresden, since it's only a two hour ride there direct. Now, if you want to do a day trip while staying in the Czech Rep, then choose a place near Prague.

In 2016 I finally decided to stay in Dresden for a few nights, finally used that chance to do a day trip to Prague...interesting seeing landscape the train route took on those two hours.

It depends on your interests. Dresden has some of Europes best museums, and they are quite unique too.
Green Vault
Old Masters
Porcelain Collection
Cabinet of Mathematical and Physical Instruments
Armoury with Turkish Chamber
The reconstructed part of the old town however is very small, but offers some unique structures like the Zwinger.

If you are not into museums but prefer to see "Old Europe" Cesky Krumlov or Kutna Hora, which is closer to Prague, are better ideas.