re: Recommend me some places to travel alone.

If you are into history and willing to travel alone expand your options to include Normandy. I went alone (wife couldn't come on business trip I had to Amersfoort, NL) and I got way more out of the trip by doing things in Normandy that I wanted to do. I'd recommend Bayeux as a home base if you decide to do it. Flights to Paris aren't too bad, or you can fly to AMS and train to Par.