This Vault is located on the Western edge of the Capitol wasteland. It has the highest amount of radiation in the game, peaking at 3500 rads.
Vault 87 cannot be accesed from the surface, although it can be reached with an advanced radiation suit and around 250 radaway. The door is inaccessable and is heavilly guarded. There are suitcases and a dead scientist down there. There is only a radiation suit, radaway, and a .32 pistol there.
The Vault can only be entered through Little Lamplight, either via Murder Pass of secondary entrance. Murder pass can be entered no matter what you do, and is good for experience but not on your stimpacks. The Seconday entrance is in the back of the Great Chamber and can be activated by Joseph after Mayor Macready tells you about it. It requires and average science skill to hack.
NOTE: This is assuming you entered through the easy entrance, not murder pass.
You will be in a small chamber with a door on the left. Enter it and read the terminal if you wish. Exit into the hallway and go straight, ignore the stairs for now. The small cave with the mannequin contains a Nikola Tesla and You in the crate at the feet of the mannequin. Exit the room and go up the staircase.there is a door to your right, this leads to Murder Pass, If you came through the pass, this is were you will start. To the left (or straght from the pass) is another door. kill the radroaches with a Melee weapon. THIS IS IMPORTANT! Enter sneak mode and go down the next hallway, stopping when you hear voices. This is a scripted Super Mutant conversation. Kill them when you wish, and continue up into the Living Quarrters.
Continue up the stairs until you reach a large chamber. Enter the Atrium and clear the lower level. Proceed to the upper floor, getting health from the bathrooms if nesesary. If you have 100 lockpick and don't want to fight mutants, go through the first door on the left at the top of the stairs. It will allow you to skip a small ambush. On the other side of the atrium, turn left down the stairs to the engineering station. Kill the mutants and use the terminal, reading entry #007 to open a wall safe. Back upstairs, continue until a locked door on the left. This is a storage room with quite a hall of items including a Nuka Cola Quantum and a Pugilism illustrated. at the top of the next flight of stairs, there will be mutants past the barricade on the right. further down the hall, the opening to left leads to a collapsed tunnel and radiation. Watch for a mutant in the medical room, then search the safe. [TIP: pick the lock and then hack the safe for double experiance. This can be done anywere with a terminal that unlocks a door or safe.] Then go up the stairs behind the barricade and enter the Test Labs.
There will be a mutant in the room to your immediate right, and some supplies for your journey throug the vault. Continue along, and check the test chambers for a grueseome surprise. When you hear the intercom, walk up to Fawkes and agree to help him, or kill him with the terminal next to the door. If you decide to help him, (RECOMENDED) go right and down the isolation hall. Kill the mutants in the end room. Tripping the alarm will open ALL cells, while the terminal above the fire alarm will only opern cirtain cells. Follow Fawkes through the Vault, until you arive at the GECK Chamber. Go back the way you came, and you will be ambushed by the Enclave, who knock you out.
In 2077, when the bombs fell Vault 87 suffered a direct hit. The interior was undamaged, and the experiment went on as normal. The death toll rose as more people were draged to the test labs and mutated into supermutants. They eventually broke out of the holding cells and mutated or killed the rest of the Vault's population. Vault 87 has been all but forgoten due to the radiation and mutants, The Vaults seals laked, and the GECK chamber has been flooded with radiation. It is almost holy ground to the mutants, and they feircely fight for it. It is also the repository of items gathered on wasteland excusions, and were all ccaptive are taken. The FEV stores have gone dry, and the mutants are in the wastes in larger numbers in order to find it.