Search map keyword Clandestine.
It's an underground Spartan Training Grounds. Set in a cave, this map contains 4 different bases, Red, Blue, Yellow, and Purple. Each base has a BR, Yellow and Purple have a sniper and a shotgun. While Red and Blue spawn with an additional 2 rifles commando and breacher br. If someone or 343 made a workable multiteam gametype, then you could use that, but till then, I have added it Neutral Flag capable. Works well with CTF, KotH, Oddball, Attrition/Elim, Neutral Flag. Bots work, but they are stupid with the layout. Have NOT setup FFA or Strongholds yet. Works up to 6v6.
Sorry this is the most pictures I could get on this site. Also some of the colors and materials I've noticed have been glitching. It seems to do that when you touch up things and republish.