The zoo can be driven around because it is very big, and the road actually goes through the middle of the aviaries. You can probably judge the size here by the fact that the road would be just over two cars wide, and the aviary reaches to the very top of the photo. The roots of climbers which are hanging down from the tunnel are obviously above car-height, and well above my head-height (six foot).
The aviary stretches well back into the distance and the road curves a bit so you can't see the other end of the tunnel when there.
For visitors, there are raised walk-through (meshed) tunnels through the right-hand side of the aviaries (as in, the right side from the perspective of this photo). The left side cannot be entered. This whole section is one giant aviary with several species of hornbills inside. It slopes to the right (on a hill), so the right side is even taller inside than it appears from this photo.
At the far end is another smaller (but still huge) aviary, also walk-through, with more hornbills and includes a couple of sectioned-off areas for breeding pairs.
