Our first full day in Kuala Lumpur was pretty jam packed. All up, we were wandering around the city for about 12 hours, and visited the Malaysia Tourism Centre (grabbed some brochures and enjoyed their air conditioning), Petronas Towers, Suria KLCC Shopping Mall (just got ourselves some lunch there), walked through KLCC Park on the way to KLCC Aquaria, headed up KL Tower for a view of the city before wandering past Masjid Jamek mosque and through Central Market.
The aquarium was a great spot to visit, and we had a great time wandering through the wide variety of exhibits they had n display. The piranha tank when you first walked into the aquarium was rather good, as were the otters and the large section dedicated to fish from the Amazon (some of them were massive!). The view from the KL Tower was also good, and as an extra bonus, was cheaper and much easier to get into then the Petronas Towers observation deck.