Many years ago I visited Bukit Lawang in North Sumatra and saw the Orangutan at the Orangutan rehabilation centre there.
I read that they rehab centre has closed down. Can you still see the orangutan close to Bukit Lawang?
is there any where else in Sumatra where you can do jungle trekking to see the Orangutan?
The Organutan Rehabilition Centre closed down more than 10 years ago as they found that the jungle around Bukit Lawang was saturated by Orangutan so they could not introduce any more Orangutan into the wild in that area.
They still have a feeding platform which the rangers go to every morning and every afternoon to provide food to any of the reintroduced orangutan that may need to come back for a free feed.
The feeding platform moves locations every few weeks but it is about 20 minutes walk into the jungle from Bukit Lawang.
There is still a good chance to see the orangutan if you go for an extended jungle trek but no guarantees. If you are lucky you will see them.