Hamilton's Hideaway

 is a small cave in the side of a cliff face in the Capital Wasteland.

This underground complex appears to be an abandoned military or medical research facility.

It is mentioned by Sheriff Evan King in Arefu as a possible location of The Family as part of the Blood Ties quest.

Three Dog will also tell you of this location and give you a key to the hidden weapons cache inside after you help him restore GNR's broadcasting capabilities, but only if you have either The cache is behind a cell door (key-required) in the northwestern-most area, behind some rubble. Use the key Three Dog gave you to gain entrance.
 * met the speech check when first getting the mission from Three Dog or
 * already talked to Doctor Li about your father's whereabouts before completing the GNR quest.

Location

 *  can easily be found by traveling about a mile NE of Arefu into the river bed and following the cliff's rock until you find the entrance.
 * It's just north of Moonbeam Outdoor Cinema and just southeast of Northwest Seneca Station.

Enemies
The cave itself is populated with Radscorpions, Radroaches, and two Raiders.

Some of these enemies will be dead when you find them, because Radscorpions and Raiders will fight each other. Also, because the cave is quite dark in most places, even a character with very low sneak skill can easily pick off enemies from afar with Sneak-Attack Critical Hits.

Scavenger
Just west of Hamilton's Hideaway, in line towards Arefu map marker, is a small metal shack with a Scavenger.

Notable Loot

 * Duck and Cover! - in the room with the Raiders; also note the Cherry Bombs on the counter.
 * Bottlecap Mine - in the same room as above on a Workbench.
 * Nuka-Cola Quantum - in the same room as above.

In the weapons cache
You'll need a key to get in. See note about Three Dog above.
 * Guns and Bullets - on a table
 * Mini Nuke - on a shelf
 * Stealth Boy - on a shelf
 * Assault Rifle
 * Combat Armor
 * Combat Helmet

Appearances
appears only in Fallout 3.