Big Darwa Fort
The Big Darwa Fort is situated at the entrance into the Udam land. It is a very heavily fortified fort and can be a real challenge if you don't have the later Skills or upgraded equipment. It IS doable with a lower level Takkar.
You can approach this fort just like you approach any outpost. But expect it to be a lot harder. The fort has a center area with smaller areas to the left and right. If you want to take on this fort by regular means, you must move around very stealthily since facing all the troops plus reinforcements will be very difficult.
Scout all the areas with your owl, and if possible, use the bombs the owl has.
Also remember that your beast may make or break stealth runs. If you want to do better at stealth, maybe consider on dismissing your beast since it can alert enemies unintentionally.
Another VERY important skill if you decide to take on the fort with just yourself, you should get the Heavy Takedown to be able to eliminate the elite units. Without it, alerting the base is almost sure-fire.
A special elite unit can be found. This is Dah. He has a rhino helmet unlike the others (although its hard to distinguish. The most notable difference is having an HP bar. When you engage him or go near him, an HP bar will appear. You must defeat all the enemies to capture the fort.
The easiest way to capture this fort early is having the skill Mammoth Rider. It can be obtained from Karoosh and his skill tree. There are a bunch of mammoths outside the camp so you can get one there and go to town on the fort.
Riding on a mammoth is basically easy mode so just waltz into the fort and mess everyone up. Do note that both you and the mammoth are NOT invincible. You can still die if you get too overconfident.
After capturing the fort, you will see a little cutscene involving Dah.
You will tell him to teach the Wenja how to make the poison bombs.
Congratulations on getting a new specialist. Not only does he teach you how to make the Berserk Bombs (Which are amazing), his skill tree is ridiculously good so get on with building his hut.