Supernova Island is the second island open for exploration in Mother 3.5. It is a very touristy area. Supernova is the urban settlement by the seaside where most of the population is. As a result, Supernova Island is a hospitable place. You can even get your own house here (not counting your house in Nova Village.) There are two mountains on each end of the island, forming a tight pass which is watched over sternly by the Pig Army. Beyond that point lies the Supernova Crater where Thunder Tower is located. Each mountain area has something located near it as well. The eastern mountain is home to the Factory and the western mountain hides the Second Cave of the Future. The mountains are treacherous and are avoided by all save for daring explorers. The crater is off-limits, but perhaps you could still find a way in there.
Much later, in place of the Factory, there is a dungeon called the Abandoned Factory.