Belgium Netherlands and Luxemburg together count as 1 country (BeNeLux)
Croatia and Slovenia together count as 1 country (Croatia/Slovenia)
Austria and Liechtenstein together count as 1 country (Austria)
France and Monaco together count as 1 country (France)
Bulgaria, Serbia and Montenegro together count as 1 country (Bulgaria/Montenegro/Serbia)
The following countries count as 1 country each: Denmark, Finland, Germany, Greece, Hungary, Italy, Norway, Portugal, Republic of Ireland, Romania, Spain, Sweden, Switzerland
You can travel between the countries as much as you like. If you want to travel from Germany to Switzerland to France, and then back to Germany, that still counts only as 3 countries.