An Icon for KL is the Petronas Towers, from 1998 -2004, they were the tallest buildings in the world and still are the tallest twin towers. The highest accessible floor is at level 88 with the Sky-Bridge at levels 41 & 42. Tickets to the top can be purchased on-line , HERE, or from the office at ground level. Cost at posting this was MYR 85 or around $30 AUD, be sure to plan ahead as they do sell out very quickly for the more popular times- Open from 9 AM - 9PM every day but Monday when it is closed.
The water features and park at the rear are popular places to hang out and enjoy a bit of open greenery in this huge metropolis. At night the fountain sound and light show is worthwhile and while perhaps not being in the same league as the Burj Kalifa one in Dubai has been around quite a bit longer. The shopping mall, Suria, underneath the Towers is quite huge with more than enough designer labels to satisfy the most ardent follower of fashion. As well there is a reasonably cheap food mall as well as a decent sized grocery store "Cold Storage" in the basement.
We have never bothered taking the lift to the Sky Bridge in the Towers as have thought that the view from there without the Towers in view would not be as spectacular without them. Our suggestion is to spend the saved money on a drink or two at the Sky Bar in the Traders Hotel which is within a 10 minute walk of the Towers on the other side of the gardens next to the Aquaria KLCC. It's not the swankiest place and the drinks a little overpriced but the view is spectacular and they do have happy hour specials during the week.
If you do your homework well and are staying anywhere within the "Golden Triangle' of the city centre then it is more than likely your apartment building or hotel may have a rooftop pool and even a gym with views of "the Towers" anyway. Our first apartment we stayed in last trip had magnificent views of the Towers and we spent many an evening watching the lights come on as the sun set over a "sundowner" or two.