This place is most notable for being the area shortly before a battle with one of the five super mutant behemoths. Players will generally emerge at Tenleytown/Friendship station or Metro Junction. There is generally a series of fights with super mutants all the way into the ruins of a building south. The ruins have a small doorway at the far south end which open up on to the GNR building plaza and trigger the behemoth battle.
Three bottles of purified water are in the Pulowski preservation shelter just north of the Tenleytown/Friendship station entrance.
Three suits of power armor and helmets can be gathered in the area: One suit of armor can be taken from the body of Initiate Jennings along with his helmet laying beside him, another suit of armor and helmet can be taken from the dead Brotherhood of Steel knight sprawled on the fountain, and finally Initiate Reddin's armor and helmet can be collected after her death.
Walking towards GNR building plaza for the first time will trigger a battle between super mutants and Lyons' Pride trying to protect Galaxy News Radio. However, if you have already found James, or have been to Project Purity or Rivet City, neither Lyons Pride nor the Fat Man show up at all, which makes the fight with the behemoth much more challenging. The behemoth arrives as soon as you step out into the plaza in front of the GNR building, whether or not Lyon's pride helps you out or if the Pride isn't there.
If you have Broken Steel installed and have completed the main quest, in Chevy Chase East next to the subway a large crate will appear inside a bus shelter full of barrels of Aqua Pura. The crate is guarded by a super mutant overlord.
Just outside the downstairs to Tenleytown/Friendship station, there's a small square with a monument that is a reference to Interplay (the original publishers of Fallout 1 and 2). The bronze Earth with a circling rocket appeared prominently when launching Fallout 1 and 2. It was originally the logo for GNN before Interplay adopted it as their official logo.