Graymaze is a level designed by Richard "Levelord" Gray in the leaked Blood alpha.
This map is a maze of sorts, but it's divided into distinct areas instead of being one giant labyrinth. Two of the mazes have hidden areas in them, with one of them requiring noclip to leave it. As this is an early Levelord map, expect a lot of incorrect textures.
The "gray" in the map name is Levelord's last name, Gray. The levels with "gray" in their names are older than the ones with "gm" in them.