In the …X-Plane 12\Output\logbooks folder there is a file called X-Plane Pilot.txt. This file contains a logbook of all your flights. While it is easy to view it from within X-Plane (File –> Open Logbook) it may not be so easy to visualize since all you see is text information arranged in columns and rows. For better visualization, there are two very useful apps that can use this file. Try them both out.
The first is the VSKYLABS Logbook visualizer. This free app (get it here) provides an global map overview of all the airports you have visited. A sleek and polished app. Thank you @VSKYLABS
You can also use the full power of Little Navmap (also free) by importing this file directly into Little Navmap where it will create the logbook file inside LNM. Using this panel you can quickly go to the airports you previously visited by simply clicking them. You can get Little Navmap here. Thank you @albar965