I might put my two cents in about one of my favourite exhibits for orang-utans. Melbourne Zoo's fantastic exhibit is pretty unique and allows for 6 orang-utans and a family of siamangs to move around three habitats.
I've looked through the gallery for some photos to make a little virtual tour.
The first view you get is from a distance across a lake although you still have a fair way to go before you get there because Trail of the Elephants is in between here and there.
http://www.zoochat.com/51/melbournes-orang-utan-sanctuary-29259/
Once you're sick of the elephants you finally get to the beginning of the Orang-utan Sanctuary. The first view is into the large netted exhibit. It's full of thick trunks, ropes, platforms, and enrichment stuff and the large surface area of the netting means that the apes have a whole lot more climbing opportunities.
Here's a photo of the approach to the netted exhibit.
http://www.zoochat.com/51/melbournes-orang-utan-sanctuary-29260/
And here's a photo of the actual netted exhibit. The metal part in the front of the exhibit is one of the locations where keepers do demonstrations during the day.
http://www.zoochat.com/51/melbournes-orang-utan-sanctuary-29261/
After this you can into the indoor part of the exhibit. This space is a really effective area because it accommodates large crowds and during the summer it presents one of the few cool places to escape the heat. Windows on both sides of the pavilion offer views into both of the outdoor exhibits.
http://www.zoochat.com/51/melbournes-orang-utan-sanctuary-29262/
Towards the back of this exhibit is the double height indoor exhibit with another presentation point and one of those interactive puzzles with the sticks and treats. I couldn't find a photo of just that exhibit though...it's at the back, in the left, of the above photo.
The last part is the largest and, in my opinion, best part of the exhibit. It is a huge, open-topped exhibit with a moat along the front and wall along the back and it's viewed from a high boardwalk so you can see into treetop level. This exhibit also has one of my favourite features of the whole area. Heaps of fibreglass sway poles are scattered around and allow for the apes to move around the exhibit without having to lumber around on the ground. There are heaps of photos in the Melbourne Zoo gallery if you feel like trawling through it but I'll include some of them that show it in the best light (

).
http://www.zoochat.com/51/melbourne-zoo-july-2009-a-90423/
http://www.zoochat.com/51/orangutans-sep-2008-a-78101/
http://www.zoochat.com/51/melbournes-orang-utan-sanctuary-29267/
http://www.zoochat.com/51/melbournes-orang-utan-sanctuary-29271/
Hope you enjoyed.