Google Earth is a really fantastic tool with a ton of fun uses, both inside and outside of the classroom. Originally created for the CIA, the tool was purchased by Google and then released to the public in 2005. Since that time, it has gone through numerous changes and iterations, constantly building in depth and breadth of function.
Google Earth comes in 3 flavors (4, if you count the professional version): A desktop app, a Chrome plug-in, and a mobile app. I really see no reason not to use the desktop app if you can.
Google has a searchable / browsable database of all sorts of maps (not just historical). You can download these maps or buy print copies of them, but you can also view them in Google Earth.
You could just do a Google Image Search for photos of famous sites you want to show. Or, you can go there with Google Earth.
When I taught World Geography, I used Google Earth to help teach a variety of objectives, such as seasons and latitude and longitude.
You can also use Google Earth to show other Geography objectives, such as urbanization, irrigation, deforestation, etc. These gifs were made with Google Earth as part of a joint project between Google, NASA, and Time Magazine: