Aqua Arena
Arena is correct term but, oh so much more. This is a very spacious & complicated layout with pathways, off shoot areas, water areas, secret things, per the author, and King of the Hill play. Has been tested primarily with two players, recommends 8 easily. Mr. Ogle states he was looking to build a simple design. Don't think so! Aliens of every stripe so solo players don't fall into boredom.
Levels in map "Aqua arena v1.0":
Aqua Arena