X-66 Hexcrete archipelago is a location in Big MT in 2281. It is directly north of the Z-38 lightwave dynamics research station, southeast of the X-13 research facility and west of Z-43 innovative toxins plant.
It is made up of large hexagonal structures sticking upright from the ground, ranging in height from shorter than the Courier to several stories tall. There is also a pool of radioactive liquid that emits 1 rad per second. Two packs of night stalkers spawn to the south and east, in range to attack. In addition, its proximity to the X-13 research facility means that any robo-scorpions guarding it will attack the player character when venturing north from the location.
- A bedroll is located just southwest of the map marker. A duffle bag and camera are next to it with a skeleton.
- There does not appear to be an entrance to the structure or purpose for the location other than a fast travel point.
- Multiple Y-17 trauma override harnesses can be found roaming the area.
- The pipes surrounding the area are riddled with frag mines.
- A cut ending to Old World Blues would have said: "Goodsprings was crushed beneath bizarre hexcrete blocks that stacked to the sky." However, this still does not explain what the blocks do.