The astronomical clock in the Old Town has a moving display, on the hour. Get there early. Good subway and bus system. Prazska Loreta is AMAZING> There are jewelled vestments and chalices in a room with a guard. A 90cm monstrance made fromgold and silver with 6,222 diamonds. SEE IT! Can get there by bus. Closes 12.15 to 1 pm. Lots of other things there, it's a place of pilgimage.
St Nicholas Church in Old Town Sq has a magnificent chandelier. Boat trip is very cheap, for an hour, very pleasant.
Yes, St Vitus Cathedral at the castle has wonderful stained glass windows. Need a ticket b4 you queue.