The Lego City Sewers
I think this is perhaps the best of The Unknown's four "Lego" style maps, which form the map pack: the other three are Lego Courtyard, Lego Monastary, and Lego Underground, while the "Lego" texture is also part of the pack - though if you have already got BlockBuster, then you already have all the textures you need. This map comes up on server lists as City Lego's Sewers, by the way!
This is a nice place to play, with room for two to six players. That white, blurry bit isn't a teleporter, I should warn you - rather, it takes away a bit of health if you move through it, the opposite of a "healpod"... It is also possible to fall to your doom here, so be warned! Of course, if you do leap across in a suitably agile fashion, you will have grabbed the whomper - but I think the two whomper batteries are a bit too hard to grab hold of without making that fatal plunge!
In some ways this is a more conventional NAB map than the rest of the pack, but it is still an excellently-built fighting arena, adding a bouncer to the mix, and some narrow ledges, plus a shield in a box, and some cool views out of the windows. So if you have read this far without downloading that nice juicy pack of maps... time to get with the plan, okay?