The Petrin Tower is on the West side of the River Vlatava and overlooks Prague from a great height. Take a 22 tram round the back of the Palace, go through the Monastery and have a beer and some lunch, then a 15 min walk to the Tower. You dont have to climb the Tower if the queues are big because if you walk on past and down the hill a little way, you will find at the second stop of the railway a restaurant, also a good outdoor cafe and viewing area, sit and enjoy the sunshine and the view which is really good. Toilets there too. Don't forget to have a valid and validated metro ticket for the railway 5 minute journey down to the street level and the trams, with you, or you WILL be fined.