If you are interested in European travel, keep in mind that it should be whatever you choose. No one knows better than you what your money and time limits are OR what interests you most.
Get a handle on your finances before making a plan. Each level of European travel requires a different financial outlay. When you choose small, out of the way destinations, you will find less expensive accommodations and often less expensive meals and fares as well. Trains that take you to large cities can drop you off in small ones to spend the night. Shopping markets for daily meals can keep your costs down considerably.
Another important financial aspect of your trip will be exchange rates. With the Euro as the main currency in sixteen or more European countries, the ratio of Euro-to-dollar will be important. England retains its own currency. The English pound measured against the dollar may be another factor in your decision. Or, you may want to research the exchange rate in Eastern Europe. The former Soviet states have the same beautiful architecture and interesting histories as their better-traveled Western European neighbors.
Also look at travel costs to European airports. Some have better deals than others. This can be like an invitation to discover the area. Renting a car is not necessary if you can rely on public transportation like buses or trains. With financial considerations in mind, you can plan and enjoy an extensive trip without the benefit of a pricey tour. Even boat travel is possible by choosing ferry routes over pricier tour boats.