First of all its not really truth, that you can travel freely with an visa of an Schengen country
http://is.gd/CcQERk
the first line in the visa must have written "Schengener Staaten" or "Stati Schengen" or "Etats Schengen" or in czech "Staty Schengenu" only then you can travel freely in the Schengen area. It is not often the case but it might be stamped "D" or "F" or "E" or an "CZ"
There are some more lines you have to check, look at the line where in the picture above is written "MULT" that is the line who actually says how often you can enter Schengen area, if there is written an 01 or 02 you might need a new visa. With MULT what means multiple you can go in and out, how often you want during the time which is noted in the line above.
So in the case of our own Igor, it was only allowed for him enter 1 time, during 6th and 26th of February the Schengen area and stay for 6 days.
So if you have an Schengen visa and want to travel with it please check it! If you need help, just ping me
br gnokii