Kota Kinabalu is home to the highest mountain - with the same name - in South-East Asia. The area is not just known for the climb to the top, but also for diving spots and a lot of nature.
Kuala Lumpur is the capital of Malaysia and the economical and cultural center. Best known are the PETRONAS twin towers, but there is also the Petaling market where you can lots and lots of branded, but not original bags, shirts, parfum, etc. Quite interesting is also the birdpark, where the birds have free entrance to the restaurant... And a real highlight are the Batu Caves with Hindu background!
Georgetown is the capital of Penang Island and known for historical buildings, Chinese Shophouses, Mosques, art and good food.
Kuching is the main city on Sarawak, the northern part of Borneo that is part of Malaysia. There are many proboscis monkeys (with a big nose) and some national parks worth a visit.
Melaka has a long and very interesting history, where it was part of the major trading route between Africa, India and Indonesia. Most tourist attractions are reminders of this rich past. The Dutch occupiers left some graves and the Stadthuys, both with "old Dutch" writings.
The Cameron Highlands is known for tea estates, orchards, waterfalls, nature, wildlife and golf courses. It is one of the oldest tourist spots in Malaysia.
The Gunung Mulu National Park is a UNESCO World Heritage Site that encompasses caves and karst formations in a equatorial rainforest setting. The park is famous for the Mulu Caves and natural tunnels.
Johor Bahru, as part of tihe wider Iskandar Urban Area, is a city of 2.5 million people. It's border with Woodlands/Singapore is one of the busiest crossings in the world.