Yao Guai Tunnels

The Yao Guai Tunnels are located due west of the Charnel House, and northwest of Smith Casey's Garage. The entrance is a chain-link fence door in a rocky outcrop. In a wild turn of events, the caves are inhabited by a number of Yao Guai.

Notable Loot
There is a Pre-War Book on the picnic table just as you enter the Tunnels, and a random weapon behind a pile of sandbags next to the picnic table, in the cabinet.

There is also a bottle of Nuka-Cola Quantum sitting on a picnic table on the way to get the Bobblehead - Sneak (see below).

A Stealth Boy can be found in a Very Easy locked footlocker in the south chamber. (Appears to be random loot.)

Floating in the pool of water next to the bobblehead is a settler's corpse containing the Yao Guai Den Note about setting up camp in the tunnels.

In the southern section of the Yao Guai Tunnels there is a Grognak the Barbarian book along with a dead Raider on a high ledge on the south wall (accessible as you exit from the "Yao Guai Den").

There is also a dead Mercenary leaning against the large rock just before you exit the "Yao Guai Den" and a dead Settler and dead Wastelander in the milky pool in the "Yao Guai Den". Additionally, there is another dead Raider on the ledge overlooking this pool and a dead Wastelander in the hole of the rock column just above this pool. The latter (dead Wastelander) can be accessed by jumping on the metal shelves on the side of this column opposite the pool. No delicious booty on these turkeys though.

Bobblehead Location
To find the Bobblehead - Sneak, turn north at the first major intersection and follow the tunnels to the door to the Yao Guai Den. Once inside the Den, walk straight ahead to the central pillar, and then head to the left. Immediately look for the natural stone ramp that leads along the eastern edge of the cavern, overlooking a crescent-shaped pool of water. At the base of the ramp is a Metal Box with the bobblehead standing on top of it.

Watch out for bugs: you can get stuck in between rocks on the edges of the cave so save your game before exploring the edges.

Enclave Outpost
After the quest "Waters of Life" you will find an Enclave camp directly east of this position. They are all dead, with clear signs of a struggle all around. They may have been studying the Yao Guai for ways to control them similar to the Enclave Deathclaws, or may have simply not known about the Yao Guai den when they set up the outpost.

I found this camp after the "Waters of Life" quest as well. However, the enclave soldiers were still alive, at least until I got there. (XBOX 360 Version)

YouTube Videos
Gameplay video & Sneak Bobblehead Location EFCDr7QWV98 SfR-FAKkwVg