Spend a day or more Rafting down Wampu River on a rubber boat, cost is 65 euro/person minimum three (3) persons.
Floating along the Bahorok River, which is about 12 km and will take 2-3 hours on inflated tube. These can be rented at numerous locations. Stop at the bridge and return to Bukit Lawang by local transportation(public transport). Check the river condition before you start tube-rafting down the river. Tube rent for is Rp. 10.000,- and public transport back to Bukit Lawang is Rp. 8.000/person.