St. Marks Basillica is located in St. Marks Square and is a sight to see. The outside is amazing looking, but just wait until you walk inside and look up. The golden mosaics cover the whole inside of the building and are quite amazing! You can go in for free, but if you want to go up to the over look area and museum (which I recommend) there is a charge of 5 Euros per person. Here is a view from the balcony on top of the Basillica.