The Vault entrance
Above ground, the radiation near the entrance to Vault 87 peaks at well over 3,000 rads/second, which is fatal in a third of a second. According to information obtained from the Garden of Eden Creation Kit, the Overseer's terminal states, "I'm quite sad to report that due to a direct hit from what I presume to be a nuclear weapon on the entry area of Vault 87, we will be unable to provide the Scouting Reports as outlined in Vault-Tec's Operations Manual. The main door to Vault 87 is damaged beyond repair and we are detecting extremely high levels of lethal radiation outside and in the entry tunnel."
It is possible to reach the entrance through the extensive use of RadAway in combination with clothing providing radiation resistance and/or Rad-X. However, as the Overseer's message mentions, the door is inaccessible, making the Vault impossible to enter from above ground. The map marker will activate near the entrance. Dead scientists in radiation suits can be found near the Vault door, as can RadAway, presumably carried by the scientists but not enough to prevent their death by radiation poisoning.
An Eyebot is usually seen patrolling south of the entrance.