Yao Guai Cave (Fallout 3)

The Yao Guai Cave is a small cave that can be reached by going through the Cliffside Cavern Raider outpost. If you fight through all of the Yao Guai, at the end of the cave you can find schematics for the Nuka Grenade.

Alternative way
The alternative way to reach the schematics is to simply jump down to the cavern floor below where the one Yao Guai is running. Kill it and proceed to take the schematics, which are placed next to a few skeletons. Now, go back to where you jumped down. On the side of the cavern, you should see rocks that you can jump and walk on. Navigate your way up and you will find yourself back at the exit/entrance. This way, you can skip fighting 2-3 Yao Guai, unless you attract them somehow. Make sure you don't let your follower take the long way around to catch up to you. best to just let them wait at the entrance to the caves.