The swoof planet is an alternate area to the village accessed by building the rocket ship, three area expansions are accessed by building bridges, another few are accessed by using the magic bird and stardust. There are many swoop only items and plants e.g. Candy corn, star fruit and moon cheese.
Swoof huts are available to build after completing constelotions in the obsevertory hut.
Similar to the mountain, you can excavate craters for stardust, complete stars ( to fill constellations ) mystery eggs and mystery seeds as well as xp and coins