One of the most popular touristic locations of Monaco is Prince’s Palace of Monaco, in French Le Palais des Princes de Monaco. Even if it is not a big palace, this is one of the most important place in Monacco-ville.
Apart from the palace itself, its located on a high hill where you can take nice photos and enjoy the view.
You can find the detailed info in this page: www.palais.mc
After Prince’s Palace, you can walk down to Oceanographic museum