At present (August 2008) a new wharf is being built so a small temporary one is located at the west of the town. All boats from Sibu arrive here - previously they were split between different docks depending on destination.
As of Jan 2011, there are no speedboats heading North to Belaga due to a new dam up the river. Alternate routes include heading back to Sibu and taking a bus, or trying to arrange smaller boats and 4WD vehicles (though this could be costly).
As of Jan 2012 it's possible to take speedboats to Belaga, since the dam is completed. You need to apply for a free of charge permit at the Residents office in Kapit near the airport. Therefore you need to stay overnight in Kapit before heading to Belaga. It's possible to take a 4WD from Belaga down to the main road at the coast.
There are some longhouses close to Kapit. But be cautious with guides in Kapit, as you'll just be overcharged for transport/housing that you can find on your own at the local wet market. Be cautious about a friendly Mr. Joshua Muda Guna, who is wrongly mentioned in some guide books as reliable and knowledgeable. His tours are expensive and you don't get what he promises.
From Sibu there are regular AC express boats to Kapit (3 1/2hrs, costs 25RM per person for the economy class, 30RM for the 2nd class and 35RM for the 1st class). The last boat leaves at 2:30PM and arrives in Kapit anywhere between 5:40 and 6:30pm depending on river levels. Boats can get a little chilly so consider bringing a jumper.
If you ride a motorbike, you can take it on the boat with you for another 50RM (be ready, it's not easy to bring the motorbike from the boat to a pier in Kapit. They will ask you to pay for their help to bring it up the stairs. Do not agree, there is a way you can drive it avoiding stairs, just go to your right along the shore)
There are minibusses close to the wharf.
Vist a longhouse, like the 100+ year old Rumah Bundong (formerly known as Rumah Seligi after the late chief). For a few hour tour during the day, just head to the wet market (big outdoor square selling fish and other assortments) and talk to one of the yellow cab drivers. William Taba (+60138000112) will provide transport at a fair price (half price of any 'tour guide'). A minbus may run 60RM per person, and then add another 25RM pp. to the chief of the longhouse - a modest fee and some of that has to goto the state.
Longhouse Rumah John is another option. Take the 11 am boat to Pelagus and tell them you are going to Rumah John. Usually you can arrange to stay there for 25 RM per bed. They can cook for you, though the food there is limited, so better to bring some with you. There is only one boat per day, so anyway you have to stay overnight before coming back to Kapit.
Longhouse overnight stays are best to be invited, the best way to do this is to ask around to learn more about the long houses: strangers on the street, neighbors at the hawker stalls, or your hotel staff should be able to help.
Walk around the city center on the weekends - this is the busiest time when nearby locals come to visit, you'll see the city dry up around 3pm on Sunday when everybody takes the last boat out.
When in Kapit you must try some of the excellent local cusine such as wild boar (babi hutam). There are great hawker stalls that open at the Open Air Night Market one street behind the public square.