In the Loire Valley of France, you will find many marvellous chateaux surrounded by beautiful gardens.  Having visited a healthy number of these chateaux, I can say that the gardens at Chateau de Villandry were the most impressive that I have seen.  An easy 9 mile car trip from Tours will drop you at the castle car park, which is free.  Entry to the gardens will cost € 7, or for a look in the fully restored chateau as well as the gardens you pay €11.