SC2Mapster

The island in the center of the river is much more difficult to defend than the starter bases, which are both behind huge natural cliff fortifications. However, it has the richest mineral and gas deposits by far of anywhere else in the map. More importantly, if you can build a CC/Nexus/Hatchery on the island and keep it there for 20 minutes without it being destroyed, you win! However, if your opponent destroys your island base, the timer will reset. Worse, if they then build an island base themselves, you'll have to drive them off within 20 minutes...