Kappa Mountain
Kappa Mountain is the largest mountain on Yoshi's Island. It is the setting of many levels within the Yoshi series.
Kappa Mountain first appeared in Super Mario World, in which it was the location of the Yellow Switch Palace.
Kappa Mountain starred as one of the mountains in World 5 in Super Mario World 2: Yoshi's Island. As it is the only named mountain on Yoshi's Island, it may be then suggested that it is the main setting. Kappa Mountain is a common ski resort among Yoshis.
Yoshi's Story
Kappa Mountain returned in Yoshi's Story, it's last appearance. Here it was the setting of Page 3: Summit (or at least, as much as it was in Yoshi's Island). Or, more specifically, it was the setting of Stage 3-3: Poochy & Nippy and Stage 3-4: Frustration. Stage 3-1: Cloudy Climb took place at the mountain's foothills, while Stage 3-2: Tall Tower took place around an icy tower.
Residents of Kappa Mountain include many Bumptys and Ravens, along with Goonies. Many enemies in the world would later on inspire the enemies of later games such as Paper Mario. On such example is Don Bongo, a rubber monster that highly resembles Tubba Blubba. Another example is Cloud N. Candy, a cloud monster that may have been inspiration for Huff N. Puff. However, some creatures appeared only once, such as the Centipedes and the Snow Guys.