The 1K outpost refers to an outpost located at X:1000,Y:1000.
It is a little more difficult to reach than Sky City, as intermediate diagonals can't be traversed quickly by arrow keys.
1K outpost as of March 2018
A stairway leads to the 1K outpost, built by "the stairs guy". The outpost itself is fairly small compared to the Sky City. In the middle there is a logbook intended for people to write their names and current dates in, although it seems that someone has deleted all the entries recently.
Picture of Damascus during the night from bird's eye view