Originally Posted by
JamesEaston
Make sure you bring warm clothes unless you get very lucky as both these cities are usually still in the grip of winter in March

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Average high in Prague in late March is 54F/12C Average low is above freezing. I'd say you'd have to be very
unlucky to experience the "grip of winter."
Regarding your question about time spent and day trips. Unless you are a person who likes to spend a whole day lingering around a single museum (or even half day), you only realistically need one or two days to see all the major sites in Prague as they are all connected. From the Castle/Male Strana to Old Town Square to Vaclavske Namesti and the National Museum, you could do the whole (very brisk) walk in an hour. Obviously as a tourist you would do it in a day, or two. Stretch it to three to do it VERY leisurely and linger in museums.
If your goal is only to walk the path between the four major tourist sites with thousands of other tourists, completely agree with the above. But what a shame. Prague has fantastic big parks (and if the weather is nice, the beer gardens might even open). Letna, Petrin, Riegrovy, Viktov, Stromovka. The fortress, cemetery, grounds, and buildings at Vysehrad are worth most of a day by themselves. Get back into the nice old neighborhoods -- Vinohrady, Nusle, Vrsovice, among others -- and see the small local parks, pubs, restaurants, and other oddities.