We walked everywhere, the clock was a 2 minute walk from our apartment one way, the Charles Bridge 5 minutes the other direction and Wenceslas Sq about 15, so all quite close. We didn’t use public transport at all when we were there. The only lengthy walk we did was to the castle, but we took our time and got there early, maybe 30 minutes.
I had a knee problem and had to strap it up and it did get sore with all the cobbles in the old town.