Challenging was an obscure planet in the outer parts of the North Galaxy, located in the Quelii Sector. It was somewhat smaller than Earth in size, and had slightly-below-standard gravity, but the planetary day was close to standard, and the planetary year was long, lasting 491 days. It is the home of Frieza's race, the Changelings.
Challenging was considered a temperate and beautiful planet by Human standards, with a varied terrain that included coastal lakes and tar-pits, thick forests and snow-capped mountain peaks, powerful rivers and broad savannas, small icecaps and dramatic rift valleys. Even under the King Cold, however, nine-tenths of the planet remained unexplored and uninhabited, with the population limited to a relatively small area along the edge one of the three main continents, a zone of uplands and river plains bounded on one side by the un-sailed ocean and on the other by vast expanses of desert.
Although the two cultures most closely associate with Challenging were the ancient space faring Changelings and the female Saiyan group known as the Witches of Challenging, it should not be forgotten that the sentient species at the apex of Challenging's native food-chain was in fact the mighty Ura-morph.
The fact that the Ura-morph were sentient often came as a surprise to unsuspecting offworlders. It is not clear whether they had made any independent progress towards basic tokens of civilization like kindled fire or shaped tools, and their social system and lifestyle were little different from those of many nonsentient animals: matriarchal herds led by herd-mothers roamed the landscape, hunting live prey for food. But they passed on their clan histories from generation to generation, and when they formed a symbiote circle with the planet's Saiyan population in the last centuries of King Cold's reign, they adopted basic armor and weapons.
However, several of Challenging's most important species, notably the Changelings and the Saiyans, had arrived on Challenging over the millennial as the result of off-world contacts.