Using the GPS can be tricky when you don't know exactly where you are going. Especially if you are a tourist.
If you do not have a specific location in mind and you just want to cruise along a certain city, then try entering the name of the city and then CITY CENTER in the GPS.
When you get close to the city center, change the destination to POI NEAR DESTINATION and search for PARKING GARAGES. Find a garage that is close to the center but do check out closing times before you park because some parking garages, especially the ones that belong to shopping centers, close quite early.
Park your car there and get out to experience the city by foot. Or find where those Hop-on, Hop off buses start their journey and get a city bus tour if you don't feel like walking much.