An estimated 20,000 Gorillas live in an around Odzala - the highest concentration of this iconic Great Ape found anywhere.

Western Lowland Gorilla live deep in our planet's second largest rainforest, stretching across one of the most volatile and logistically challenging regions in the world. Odzala National Park in northern Congo-Brazzaville is a critical oasis of calm amongst the chaos, being perfectly safe and eminently possible to reach in a couple of days from Europe. It also happens to host the world's highest Gorilla density, the abundant Marantaceae woodland providing their optimal habitat.

Nobody knows how many Western Lowland Gorilla there are - estimates range widely and there may be over 150,000 surviving in the primary lowland forests of central Africa. There are certainly many more than the 900 or so Mountain Gorilla that are confined to a relatively small range straddling the DR Congo, Rwanda and Uganda.

Strangely however it is far easier to see a Mountain Gorilla than a Lowland Gorilla and the reason is two-fold - firstly many more Mountain Gorilla groups that have been successfully habituated to humans, and secondly Western Lowland Gorilla largely occur in places that it is extremely difficult to visit.

So what is the Gorilla trekking like in Odzala and how does it differ from the Mountain Gorilla experience further East?

There are three habituated families of Gorilla in Odzala, Jupiter, Neptuno and Pluton - all are being followed for research purposes and the first two are the ones that visitors typically spend time with - although all three groups are regularly encountered on the same trek.

Western Lowland Gorillas tend to be more active and arboreal than their montane cousins and therefore photography can be challenging - this is less about portraiture and more about behaviour. However the trek itself is unsurpassable as an experience - the group size is tiny, generally 1 to 4 guests, a tracker and a guide - there is no advance party and no bleeping radios. How it works is that the tracker, who is actually assigned to the researchers and will spend an hour with a one of the Gorilla groups every day, whether he has visitors in-tow or not, will go out alone in the late afternoon to locate the Gorillas in order to ascertain where they will nest for the night. The following morning the trekking party heads out at first light in order to catch up with them before they move too far. The terrain is not steep but the forest is thick. A point on terminology - there is Gorilla trekking and Gorilla tracking - typically the tracker tracks and the visitors trek - in many places never the twain shall meet because the trackers head off in advance of the visitors who duly trek in later. One of the great pleasures in Odzala is that as there is no advance party and therefore the guests get to see the tracker track - and they are astoundingly good, not just at finding the Gorillas but being able to second-guess where they will move next - which might be up, down or around you.

Gorilla trekking may be main-draw for an Odzala safari but it offers a huge amount more - both in terms of wildlife and activities. While it would be easy to pigeon-hole Odzala as a place only for people with a special interest in primates - and there are 17 species, including occasionally encountered chimpanzee - it is amongst the best place on earth to seek out the critically endangered Forest Elephant.

There are three camps in and around the Park - each set in a different biome - Forest, Bai and Savannah and each offering their own means of exploration - by boat or canoe, in open jeep and on foot, occasionally wading waist deep in water.

The real attraction of Odzala is getting an insight into life in the great African Rainforest - and the biggest surprise is both how accessible and benign it is - remarkably bug-free and no more hot or humid than the East African coast.