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. As expected, the caves are inhabited by a number of Yao Guai.

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.

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"). It could be approached by throwing a grenade to blow the book off the ledge. 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.

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
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.

This appears to be a random encounter location. Three Enclave soldiers may make their way to the camp shortly after you arrive. There was one incident where, instead of three Enclave soldiers arriving at the camp, three super mutant masters showed up instead. Two were equipped with Chinese assault rifles and the third super mutant master had a super sledge. Another possible event involves two raiders and a non-hostile scavenger with a minigun. Another time the enclave soldiers are found dead and the camp in disarry.

When I was between the Enclave camp & the tunnels a scavenger ran up to me and said "Some raiders strapped me with explosives!" If you choose the "Leave alone" option, The scavenger explodes. If you select the "Try to disarm" option, there's negative karma, as well as a paste-strewn gore-splosion.

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