The Sabah State Mosque is just outside KK. It's a gorgeous building, and you can visit outside prayer times. Rather incongruously, you can rent pedalos to float around the reflection pool which surrounds it.
This is a most impressive mosque and our view was limited to a minute from the rear seat of our friends' car as we slowly drove past.
I would think if you had time it would be worth visiting.
Visiting time (subject to change from time to time as to suite the prayer time):
Monday to Thursday : From 08:00am to 12:00noon & From 14:00pm to 17:00pm
Friday : From 14:00pm to 17:00pm
Saturday & Sunday : From 08:00am to 12:00noon & From 14:00pm to 17:00pm
Located a bit further south, down the road from the Sacred Heart Cathedral, this large mosque is one of the two main mosques for Kota Kinabalu. Until the construction of the Kota Kinabalu City Mosque, it was the biggest mosque in Sabah. Built in 1977, the Sabah State Mosque, it can accommodate 5000 worshippers at one time. There is also a separate balcony section for Muslim women that can take 500 women worshippers.