The Mysore Palace is an amazing piece of architecture. In fact it is India's second most famous tourist attraction after the Taj Mahal according to Wikipedia! The palace is a definitely a "must see" on any trip to South India. It is worth every bit of the 200INR it costs to enter the palace as the interior is truly amazing and many of the fixtures are covered in real gold and silver. The decor is lavish!
But for an absolutely magnificent experience the grounds of the Mysore Palace should be walked at night when the palace is illuminated by some 96,000 lights. I found the fact that these lights are incandescent light-bulbs quite surprising. The palace is only illuminated for an hour each night around sunset to conserve energy so be sure to inquire about the exact time the palace will be lit during your visit to Mysore. There is no cost to enter the palace grounds at night.