Friendship station (called Tenleytown/Friendship Station in-game, due to the fact that both stations are part of the same interior) is a Metro station on the red line. It must be traversed to get to Tenleytown station and then the Galaxy News Radio station through the Chevy Chase North exit in the south.
Grognak the Barbarian: In the back room of the small office in the northwest part of the map (map point 2). It is laying on the top left shelf of lockers on the east wall. (It's a bit hard to find; look at the picture for help)
An assault rifle in the toilet of the men's room, last stall on the left as you enter.
There is a toilet trap in the men's bathroom (at map point 1). It's in the 3rd stall on the right and gives 35 microfusion cells if it is disarmed. To disarm, jump on the toilet's tank and look down into the tank.
A pair of neutral radroaches can be found in the men's bathroom by the entrance to Tenleytown/Friendship Station, (they appear as hostile on the HUD before they're released). The tunnels' other inhabitants don't seem to bother them.
If going through the station, returning to the entrance, a dead raider and two low level ghouls may respawn.
In the southwest corner of the train station to the west of the Chevy Chase entrance, there are unusually large metal boxes that contain the usual loot. Two of these boxes stacked are as tall as the player.
To the very north, on the western track, there is a spot near the rubble that character might get stuck in. The only way out is to load your last saved game. This spot is easy to get stuck in if you try and sneak around looking for the two ghouls.
At the exit to Friendship Heights, behind the gate there is a box that can be difficult to access without using the console to disable clipping. However, this box can be accessed without console commands, if the character faces the correct part of the fence in 3rd person view. The easiest way to find the spot is to enter third person view and duck against the left wall, then slowly strafe right while keeping the reticule on the box. A few steps away from the wall the option to shearch the box should be available.
From time to time, the ghouls near the Friendship Station exit will be completely invincible (the characters attacks won't even land). Luckily, these are usually rather weak ghouls.
Tenleytown/Friendship Station only appears in Fallout 3.