I’m spending about 10 days in Borneo this September and I was thinking to divide these days in two major sights:
1) Mulu Park (to trek the Head Hunters Trail)
2) Kinabatangan River (spend some days cruising the river to see some wildlife)
Do you think these two places are worth a visit?
Do you recommend any alternative to these places, as a best option?
I think that both of these places are well worth a visit if you are interested in seeing a lot of wildlife during your time in Borneo. The only problem I can foresee is that as you are travelling within Malaysia's peak season and if you are planning on just turning up at these destinations you might find it quite hard to get accommodation or tours for next month.
For both these destinations it is best to get something pre-booked either a tour or accommodation before you arrive. For example, during your time in Mulu, there are only a couple of places that you can stay in Mulu National Park, one is government run and the other is a resort. The first gets booked up really quickly and then second option is quite pricey.
Other alternatives to Mulu National Park and Kinabatangan River could be a trip to Bako National Park to see the Proboscis Monkeys and other wildlife in the park. This can be easily arranged upon your arrival to Kuching. Another place you could travel to is the Similajau National Park where you can spot lots of different kinds of monkeys and wildlife in the jungle or spend some time on the coast and possibly see if you could spot some Dolphins out at sea! Also September is prime season to maybe see some sea turtles as they come up the shore to lay their eggs in the sand.
Mulu and Kinabatangan River are both definitely worth a visit. When I went to Mulu I just turned up and all the proper rooms in the national park were fully booked but I was lucky enough to get a bed in the dorm. However, I would agree with _Sarah_ that you'd be better off booking in adavance, rather than taking the risk on accomodation.
While you're there, as well as doing the Headhunter's Trail it's also worth visiting the caves that you can trek to from the Park HQ. Then once you've seen the caves there's a viewing area where you can hang on and watch the millions of bats coming out of the cave which is an impressive sight.
While I was at the Kinabatangan River I also did a night trek in the jungle where you sleep in hammocks and that was worth doing as well if you get the chance.
Other places worth visiting in Borneo are Mount Kinabalu (near Kota Kinabalu) which is an overnight climb but it's really a trek rather than a climb, and also Turtle island is definitely worth a visit. Bako national Park also has lots of enjoyable treks and plenty of wildlife to see, so that's definitely worth visiting as well.
But obviously the only trouble is that all of these destinations are spread out so if you're only there for ten days then you'll be limited in what you have the time to see. If you can extend your holiday at all then Borneo is definitely a brilliant place to visit, though.