This planet has a grand total of six levels:
Like all planets except Oria, it also has a hub world you can hang out in. This particular hub world is a Ghirian village, as well as some of the field near it. You can go in Dinio's house to get a few coins, as well as a funny easter egg/cameo- a picture of Pinkie Pie on the wall.
Ghiria is a grassy planet with many rivers and an ocean. It also has a volcano, and at the peak of said volcano is where you will find the first Lost Constellation.
Mario Kart Wii's "Maple Treeway" plays here. Listen: