This is one of the original Unreal Tournament maps that you get with the game, and have to play to win the 45-game "Tournament" ladder - there it is a Capture the Flag map, though one with quite different architecture at the two ends, giving, in my opinion, the red team a bit of an advantage. This remix, by Flame, looks in some areas even nicer than the original - of course, Flame does sometimes take textures from some of the more specialist UT texture sets, so it is possible that you may find you need to add extra texture files. But if you keep up with current maps, that is not too likely to be a problem!
It's a large map, with the main central divide the dock you can see above, in which a large submarine is waiting for its crew. You can climb over it, or you can swim across if you want to keep a lower profile! The flags themselves have been replaced by megapowers, as has become almost traditional; Flame may do a "target tag" version too, or maybe Tiggy will manage to cut his way through the coding problems and bring CTF itself to NAB.
So, a nice big place to explore, and good-looking too. I don't know why it has taken so long for somebody to bring this map over to NAB, but it's great to have it here now.