Path to the Courier's Mile
Maybe that's why you've come, too - need to see where the missile from Ashton touched ground down below, in Hopeville... the Courier's Mile.”— Ulysses
It is located directly under Hopeville missile silo bunker. It is basically a street that has an invisible wall hindering the Courier's forward movement, that acts as the "door" to The Courier's Mile. The map marker for this location appears after the Courier has completed The Launch quest.