[Raghavendra Rayadurga]

If you can spare a day and step out of Bengaluru but not too far then Ranganatittu is a great place as Sudhir sir suggests. In case you have only a few hours and have to be within the city boundaries then there are many lakes. I would suggest Saul Kere and/or Muthanallur Lake. Another one is Varthur Lake but may be difficult for a newbie to the city to locate and explore.