Climbing Mount Kinabalu is not the easiest thing to do and is pretty much uphill the whole way!
You start with a 6km walk to the base camp, heading off from the gate before 11am (or else they won't let you go) with your guide. Make sure you book some accommodation before you go as it is always busy.... it is also mandatory to book beforehand. There is also the problem that many of the big fish tour operators book beds without clients. Given the markup they charge on a bed, they can make money even if they don't manage to sell them all.
After a punishing walk, you get to eat and have a sleep for a little while. Around 2am, you will need to be up and start getting ready to climb to the summit. The last 2.7km is made in the dark. Your aim is to reach the summit just before sunrise. Too early, you will be freezing cold sitting on top of the windy and very cold summit.. too late and you miss the sun coming up. Gloves, a headlamp and some nice warm gear needed as you will be pulling yourself up ropes. Nothing too serious, but constantly uphill.
When you greet the sun, hopefully it will be a nice clear day and you will see a fantastic view. Take your picture near the sign showing how high up you are and then eventually start the long trek back down.
Going down is much faster, the first 2.7km is pretty easy going. Pick up your gear from the base camp, have a rest and then continue for the knee jarring 6km back down to park headquarters. Be careful as your legs will probably be very weary by now and you don't want to slip and hurt yourself. I twisted my knee going past someone on the way up, so my last 3km were very slow and very painful.
I got to the headquarters from Kota Kinabalu bus station. This turned out to be a bad idea. I nearly didn't make it for the start gate cutoff time. The minibus driver kept waiting around to see if he could get more people into his van. The van was also in very poor condition. I think the best bet is to get an express bus from the long distance bus station. These are much more comfortable and have air con. Make sure you get them to drop you off at the bottom of the hill for Mount Kinabalu National Park.
Perhaps the nicest option if you have time is to stay at the Kota Kinabalu Park the night before and then be set to go the next morning.
Climbing Mount Kinabalu is definitely a challenge. I am naturally pretty fit, but I had not done much exercise beforehand and also was suffering from the remains of a cold. I was very sore for 5 days after my Mount Kinabalu climb. There are a lot of people I walked past who I didn't think were going to make it, but saw them nearly there on my way back. It is amazing what humans can do with some mental will power.