Evergreen Mills

Evergreen Mills is located just East of Casey's Garage, in the lower left quadrant of the map in the Capital Wasteland. It is populated by Raiders and a Super Mutant Behemoth. The Behemoth is trapped in an electrified fence, which makes it quite easy to kill from a distance, as you can shoot it through the fence or take a higher position on either of the nearby train cars or the elevated walkway to kill the Behemoth. You can also destroy the generator right next to the gate holding the behemoth in to free it if you want to watch a fight between it and the raiders.

There is also a foundry in Evergreen Mills which hosts a bazaar where the Vault Boy Bobblehead can be obtained. In the highest level of the bazaar, you will find a copy of Nikola Tesla and You in the holding cell. The Terrible Shotgun can be obtained from Smiling Jack.

In order to free the slaves, you need to obtain the Evergreen Mills slave pen key from one of the raiders or from the guard house.

Due south of the canyon entrance is a mess of overturned rail cars. There is a roaming Super Mutant Behemoth in this area. Sometimes he will be nearby attacking other creatures, but he almost always makes an appearance if you stay too long near the train cars. In one car, in a closed shopping cart, is a jailed teddy bear.

Appearances
appears only in Fallout 3.

I have tried to do it both by shooting my way in, and alternately by destroying the generator of the electrical fence on the behemoth. I have found it to be much easier in the second way. Approach the compound directly from the east, get to the edge of the cliff in stealth mode and destroy the generator with the sniper rifle. you should get undetected by the guards, thus avoiding a full combat, not to mention it's fun to watch the fight between the behemoth and the raiders. In the end you can easily finish the behemoth from the cliff with a few rockets, as it usually will have less then 1/3 of life, and you will only have a couple of guards to deal with on the way in.