The following is based on Fallout 3 cut content and has not been confirmed by canon sources.
This underground complex was originally a well-prepared shelter for a family of three - a husband, his wife Maggie, and their daughter Robin, established due to a mistrust of Vault-Tec. Fitted with air filtration, chemical toilets, an artesian well, and a fusion generator, it provided a long-stay option until radiation levels subsided.
End of information based on Fallout 3 cut content.
Just north of Moonbeam outdoor cinema and southeast of northwest Seneca station, Hamilton's hideaway is a network of tunnels that sprout from one single tunnel. Multiple catwalks lead over rock which leads into a hallway constructed of metal. The weapons cache for completing the unmarked quest, Caching in with Three Dog, is located in the northwest corner of the hideaway, through a hole in the left wall.
A room with 3 radroaches in it is located around the middle of the cache and the bandit lair. 2 of these radroaches will be hostile, so will the third. The third may spawn in the wall and if you try to shoot it, it falls out of the map and appears in the room, unstuck.
Some of these enemies will be dead when the player finds them, because radscorpions and raiders will fight each other.
Sometimes 1 or 3 dead wastelander bodies (that may have spawned alive) will appear.