In short
Kota Kinabalu is the gateway to Sabah, the Malaysian state in northern Borneo. Mount Kinabalu, four thousand and ninety-five metres, is climbed in two days without technical gear and its park is a World Heritage site.
Tunku Abdul Rahman marine park, five white-sand islands, is twenty minutes by boat from the city centre.
What it really costs
Sabah is dearer than peninsular Malaysia, but remains very affordable. Housing in the centre costs little and hawker centres feed you for two or three euros.
Climbing Kinabalu is the separate item: the compulsory permit, the guide and the night in the mountain hut are booked months ahead and the daily quota is strict.
What nobody tells you
The Kinabalu permit is capped and goes very early. Arriving and hoping to climb within the week does not work in high season.
Wild orangutans are not seen from Kota Kinabalu: you need Sepilok or the Kinabatangan river, to the east, which means a day on the road or a short flight.
The city itself was flattened in 1945 and rebuilt: it has no historic centre. You pass through, you do not linger.